Diffuse lung cancer: symptoms, diagnosis, stages, and modern treatment methods

Diffuse lung cancer is not a strictly separate, official diagnosis, but a clinical and radiographic description of a situation in which the tumor process spreads not as a single, distinct nodule, but in a multiple, scattered, infiltrative, or pneumonia-like manner throughout the lung tissue. In medical practice, this term can cover various conditions: diffuse pneumonia-like adenocarcinoma, multiple foci of adenocarcinoma, lymphangitic carcinomatosis, disseminated non-small cell lung cancer, small cell lung cancer, or metastatic lung disease from another primary tumor. [1]

The main difficulty is that diffuse lung cancer often mimics pneumonia, interstitial lung disease, tuberculosis, pulmonary edema, hemorrhage, sarcoidosis, or metastases. If the patient receives antibiotics and the "pneumonia" does not resolve, if the infiltrates migrate or spread, if cough, shortness of breath, hemoptysis, weakness, and weight loss persist, the physician must consider a tumor cause. [2]

In modern classifications, lung cancer is divided primarily by histological type and molecular characteristics, rather than by the term "diffuse." The World Health Organization, in its classification of thoracic tumors, considers lung cancer based on morphology, immunohistochemistry, and molecular diagnostics, as these data determine treatment and prognosis. [3]

For the patient, this means a simple thing: the term "diffuse lung cancer" must be deciphered. It must be determined whether it is a primary lung tumor or metastases, adenocarcinoma or another type, whether there is involvement of the lymph nodes, pleura, bones, brain, liver, and adrenal glands, and whether there are molecular targets for targeted therapy. [4]

Modern medicine is no longer limited to chemotherapy alone. Lung cancer treatments include surgery, radiation therapy, drug chemotherapy, immunotherapy, targeted therapy, antibody-drug conjugates, supportive care, and palliative care, with the choice depending on the stage, tumor type, patient's overall condition, and molecular testing results. [5]

The key question	Short answer
Diffuse lung cancer is a separate diagnosis	No, this is a descriptive statement.
What is often hidden behind this term?	Pneumonia-like adenocarcinoma, multiple tumor growth, lymphangitic carcinomatosis, metastases
Why is it difficult to diagnose?	Similar to pneumonia, tuberculosis and interstitial lung diseases
What must be confirmed	Histological type and molecular features of the tumor
Main diagnostic methods	CT scan, biopsy, bronchoscopy, molecular testing, staging
The main principle of treatment	Treat not the "diffuseness" but the specific type and stage of cancer

Code according to ICD 10 and ICD 11

The International Classification of Diseases, 10th revision, does not have a separate code for "diffuse lung cancer." Codes from group C34, Malignant neoplasm of bronchus and lung, with specification of location, are typically used: main bronchus, upper lobe, middle lobe, lower lobe, overlapping lesion, or unspecified location; if the lung lesion is metastatic from another tumor, coding may differ and include secondary malignant lung lesion. [6]

The International Classification of Diseases, 11th revision, uses the category 2C25 Malignant neoplasms of bronchus or lung for primary malignant neoplasms of the bronchus or lung. It distinguishes between adenocarcinoma of the bronchus or lung, small cell carcinoma, squamous cell carcinoma, large cell carcinoma, carcinoid and other neuroendocrine tumors, unspecified, and other specified malignant neoplasms; the word "diffuse" is usually reflected in the clinical description rather than as a separate code. [7]

System	Possible code	Formulation	Practical commentary
ICD 10	C34	Malignant neoplasm of the bronchus and lung	Main group for primary lung cancer
ICD 10	C34.0	Main bronchus	With confirmed localization in the main bronchus
ICD 10	C34.1, C34.2, C34.3	Upper, middle, lower lobe	In case of lobar localization
ICD 10	C34.8	Overlapping bronchial and lung lesion	Can be used when spreading across multiple zones
ICD 11	2C25	Malignant neoplasms of the bronchus or lung	Parents' column
ICD 11	2C25.0	Adenocarcinoma of the bronchus or lung	A common variant in diffuse pneumonia-like picture
ICD 11	2C25.1	Small cell carcinoma of the bronchus or lung	Aggressive neuroendocrine tumor
ICD 11	2C25.2	Squamous cell carcinoma of the bronchus or lung	More often associated with smoking
ICD 11	2C25.Z	Malignant neoplasm of bronchus or lung, unspecified	When the type or location has not yet been specified

Epidemiology

Lung cancer remains one of the world's leading cancer problems. The World Health Organization reports that in 2022, there were approximately 2.5 million new cases of lung cancer and approximately 1.8 million deaths, making it the leading cause of cancer death worldwide. [8]

Diffuse forms are not typically identified separately in global statistics, as registries account for lung cancer by location, histological type, and stage. This means there is no precise global figure for "diffuse lung cancer": such cases are distributed within adenocarcinoma, small cell lung cancer, advanced non-small cell lung cancer, or metastatic lung disease. [9]

Adenocarcinoma is the most common type of lung cancer in many countries and is particularly common in people who have never smoked. Adenocarcinoma can develop pneumonia-like, multifocal, or lepidic growth, in which the tumor spreads through the alveolar structures and mimics pneumonia. [10]

Late diagnosis remains a serious problem. According to the National Cancer Institute's surveillance program, approximately 51% of lung and bronchial cancer cases are detected at the distant stage, and the 5-year relative survival rate at this stage is significantly lower than for localized tumors. [11]

Statistics highlight the value of early detection. For localized lung cancer, the 5-year relative survival rate, according to data from the US National Cancer Institute surveillance program, is approximately 65.5%, while for distant metastases it is approximately 10.5%; a diffuse presentation often means a more difficult diagnosis and often a later detection. [12]

Indicator	Data and meaning
New cases worldwide in 2022	About 2.5 million
Deaths worldwide in 2022	About 1.8 million
Separate statistics on "diffuse cancer"	It is not usually done
A common histological type in diffuse pneumonia-like presentation	Adenocarcinoma
A common problem	Late diagnosis
Forecast	Highly dependent on stage and molecular profile

Reasons

The leading cause of lung cancer at the population level is exposure to carcinogens in tobacco smoke. The U.S. Centers for Disease Control and Prevention lists cigarette smoking as the number one risk factor and is associated with approximately 80-90% of lung cancer deaths in the United States. [13]

But lung cancer also occurs in people who have never smoked. In such patients, passive smoking, radon, air pollution, occupational carcinogens, genetic predisposition, and tumor molecular pathways are all factors; according to the US Centers for Disease Control and Prevention, 10-20% of lung cancer cases in the US occur in people who have never smoked or have smoked fewer than 100 cigarettes in their lifetime. [14]

Radon is a significant invisible risk factor. It is a radioactive gas that can accumulate indoors; the National Cancer Institute and the Centers for Disease Control and Prevention list radon as an established risk factor for lung cancer, particularly significant for nonsmokers. [15]

Occupational exposures also play a role. The World Health Organization lists asbestos, silica, diesel exhaust, indoor and outdoor air pollution, passive smoking, radon, chronic lung disease, and genetic susceptibility as risk factors. [16]

A diffuse growth pattern is often associated not with a specific cause, but with the biology of the tumor. For example, pneumonia-like adenocarcinoma can spread through the alveolar structures, creating a pattern of lung tissue consolidation resembling inflammation, while lymphangitic carcinomatosis reflects the spread of tumor cells through the lymphatic vessels of the lung. [17]

Cause or factor	What does it mean?
Active smoking	The main preventable risk factor
Passive smoking	Exposure to the same carcinogens in smaller doses
Radon	Radioactive gas in the premises
Asbestos and silica	Occupational carcinogens
Diesel emissions and air pollution	Long-term effects on the respiratory tract
Genetic predisposition	It is especially important for some non-smoking patients.

Risk factors

The risk of lung cancer increases with age and cumulative exposure to tobacco smoke. The longer a person smokes and the more cigarettes they smoke, the higher the risk; after quitting, the risk gradually decreases, but does not immediately become the same as that of a person who has never smoked. [18]

Secondhand smoke is also important. The US National Cancer Institute emphasizes that people who inhale secondhand smoke from others are exposed to the same carcinogens, although usually in smaller amounts. [19]

Occupational risk factors include asbestos, arsenic, nickel, chromium, silica, diesel exhaust, and ionizing radiation. The risk is particularly high when occupational exposure is combined with smoking, because multiple carcinogenic factors can increase the overall harm. [20]

Chronic lung diseases can increase the vulnerability of the respiratory system. The World Health Organization classifies certain chronic lung diseases as risk factors, and patients with chronic obstructive pulmonary disease, pulmonary fibrosis, and long-term scarring require special clinical attention. [21]

A history of lung cancer in first-degree relatives also increases suspicion, especially if the tumor developed at a young age or in a non-smoker. A family history alone does not necessarily indicate cancer inevitability, but it should be considered along with smoking, radon, occupational exposures, and screening results. [22]

Risk factor	What is important to know
Smoking	The strongest preventable factor
Age	The risk increases with age
Passive smoking	Increases risk even in non-smokers
Radon	Requires inspection of premises in risk areas
Asbestos and other carcinogens	Particularly dangerous when working for a long time without protection
Chronic lung diseases	Increase diagnostic alertness
Family history	Taken into account when assessing individual risk

Pathogenesis

Lung cancer develops when cells in the airways or alveoli accumulate genetic and epigenetic damage that disrupts the control of cell division, repair, and death. Carcinogens such as tobacco smoke, radon, asbestos, air pollution, and other factors can damage the deoxyribonucleic acid in cells and create conditions conducive to tumor transformation. [23]

The pathogenesis of different types of lung cancer varies. Squamous cell carcinoma is more often associated with long-term damage to the large bronchi by tobacco smoke, small cell carcinoma typically has an aggressive neuroendocrine phenotype and early metastasis, and adenocarcinoma often arises in the peripheral parts of the lung and can be found in non-smokers. [24]

Diffuse pneumonia-like adenocarcinoma is often associated with tumor cell growth along the alveolar septa. With this growth, the lung tissue may appear inflammatoryly thickened, so the patient is often initially diagnosed with pneumonia, especially if there is a cough, sputum production, and shortness of breath. [25]

Lymphangitic carcinomatosis develops when tumor cells spread through the lymphatic vessels of the lungs. This can lead to rapidly worsening shortness of breath, a dry cough, decreased blood oxygen saturation, and characteristic changes on a CT scan. [26]

Molecular changes have become central to the pathogenesis and treatment of cancer. Some patients have alterations in the genes for epidermal growth factor receptor, anaplastic lymphoma kinase, ROS1, BRAF, MET, RET, NTRK, KRAS, and other pathways, and these findings can guide the choice of targeted therapy. [27]

Mechanism	Clinical significance
Damage to genetic material by carcinogens	Triggers tumor transformation
Lepidic growth of adenocarcinoma	May mimic pneumonia
Lymphatic spread	May cause diffuse dyspnea and interstitial pattern
Early metastasis	Particularly characteristic of small cell carcinoma
Molecular drivers	Determine the possibility of targeted therapy
Tumor immune evasion	Explains the use of immunotherapy

Symptoms

Diffuse lung cancer may not cause specific symptoms for a long time. In the early stages, the patient may complain only of a cough, mild shortness of breath, fatigue, or recurring "colds," so the disease is often detected late or accidentally during chest imaging. [28]

Typical symptoms of lung cancer include a cough that does not go away or gets worse, coughing up blood, chest pain, shortness of breath, hoarseness, loss of appetite, unexplained weight loss, weakness, recurrent bouts of bronchitis or pneumonia, and new wheezing.[29]

In diffuse pneumonia-like presentations, symptoms can be particularly misleading. The patient may have a cough, sputum, fever or subfebrile temperature, lung consolidations on imaging, and a partial temporary response to treatment, but then the changes persist or spread, requiring repeat testing. [30]

If cancer spreads through the pleura, pleural effusion, a feeling of heaviness in the chest, and increasing shortness of breath may develop. If there are metastases to the bones, brain, liver, or adrenal glands, symptoms may include bone pain, headaches, seizures, limb weakness, jaundice, severe fatigue, or impaired consciousness. [31]

Particularly concerning are hemoptysis, rapidly increasing shortness of breath, persistent chest pain, recurrent "pneumonia" in the same area, sudden weight loss, and symptoms not explained by a common infection. These signs require further evaluation rather than a blind repeat course of antibiotics. [32]

Symptom	Why is it important?
Persistent cough	A common but nonspecific symptom
Hemoptysis	Needs urgent assessment
Dyspnea	May reflect diffuse lesion, effusion, or obstruction
Recurrent pneumonia	May conceal a tumor process
Weight loss	Sign of systemic tumor influence
Bone pain or neurological symptoms	Metastases are possible

Classification, forms and stages

Based on histological type, lung cancer is divided into non-small cell and small cell. Non-small cell cancer includes adenocarcinoma, squamous cell carcinoma, large cell carcinoma, and other variants; small cell cancer is typically more aggressive, spreads more quickly, and is treated using different principles. [33]

The word "diffuse" can refer to several growth patterns. These may include pneumonia-like adenocarcinoma, multiple tumor foci in one or both lungs, diffuse spread through lymphatic vessels, tumor involvement of the pleura, or metastatic involvement of the lungs from another tumor.[34]

Staging of non-small cell lung cancer is based on the tumor, lymph node, and metastasis system. Since January 1, 2025, the 9th edition of the International Association for the Study of Lung Cancer (IASC) classification has become the standard, specifying categories for tumor size, lymph node involvement, and distant metastases. [35]

For small cell lung cancer, a division into limited and widespread stages is also used in clinical practice. A limited stage typically means that the tumor can be covered by a single field of radiation therapy, while a widespread stage denotes more widespread disease, including distant metastases or extensive intrathoracic spread. [36]

The diffuse pattern often creates staging difficulties. Multiple lesions, tumor effusion, involvement of the second lung, or lymphangitic spread can immediately move the disease into a more advanced category, so it is important for the physician to distinguish individual primary tumors from intrapulmonary metastases and inflammatory mimics. [37]

Criterion	Main options
By histology	Adenocarcinoma, squamous cell carcinoma, large cell carcinoma, small cell carcinoma
By height	Nodular, multifocal, pneumonia-like, lymphangitic
By distribution	Localized, regional, distant metastatic
By molecular characteristics	With or without changes in target genes
By stage	Tumor-Lymph Node-Metastasis System for Non-Small Cell Cancer
For small cell cancer	Limited and widespread stage

Complications and consequences

Diffuse lung cancer can cause respiratory failure. If the tumor spreads over a large area of lung tissue, through the lymphatic vessels, or is accompanied by pleural effusion, the effective respiratory surface area decreases, shortness of breath develops, exercise tolerance decreases, and oxygen saturation may drop. [38]

One complication is recurrent or protracted pneumonia. The tumor can block a bronchus, disrupt ventilation of a portion of the lung, create secretion congestion, and maintain inflammation; in pneumonia-like adenocarcinoma, the tumor itself may appear as an inflammatory infiltrate. [39]

Hemoptysis and pulmonary hemorrhage can occur when a tumor damages blood vessels. Even mild, recurrent hemoptysis requires evaluation because it may be a sign of cancer, tuberculosis, bronchiectasis, thromboembolism, or other serious pathology. [40]

Distant metastases can affect the brain, bones, liver, adrenal glands, and other organs. This leads to neurological symptoms, pathological fractures, pain, loss of appetite, weakness, and deterioration of general condition. [41]

The psychological and social consequences are also significant. Late diagnosis, the need for complex treatment, shortness of breath, pain, fatigue, fear of progression, and financial burden impair quality of life. Therefore, the modern approach includes not only antitumor therapy but also early supportive and palliative care. [42]

Complication	Possible manifestation
Respiratory failure	Shortness of breath, low blood oxygen saturation
Pleural effusion	Heaviness in the chest, increasing shortness of breath
Recurrent pneumonia	Fever, cough, infiltrate, poor response to antibiotics
Hemoptysis	Blood in sputum
Brain metastases	Headache, cramps, weakness of limbs
Bone metastases	Pain, fractures
Exhaustion	Loss of body weight and strength

When to see a doctor

You should see a doctor if your cough persists for more than a few weeks, gets worse, or is different from a typical smoker's cough. An examination is especially important if the cough is accompanied by blood in the sputum, shortness of breath, chest pain, unexplained weakness, or weight loss. [43]

Urgent evaluation is necessary if hemoptysis occurs. Even if the blood is small, this symptom should not be attributed to throat irritation or bronchitis without an examination, as it is one of the typical warning signs of lung cancer and other serious chest diseases. [44]

Recurrent "pneumonia" that does not resolve on follow-up imaging or returns in the same area requires further investigation. With diffuse pneumonia-like adenocarcinoma, diagnosis can be delayed precisely because the disease often presents as an infection for a long time. [45]

People at high risk for lung cancer should consider screening even without symptoms. The U.S. Preventive Services Task Force recommends annual low-dose CT scanning for people aged 50 to 80 years with at least 20 pack-years of smoking history, if they currently smoke or have quit within the past 15 years. [46]

The American Cancer Society also recommends annual low-dose CT screening for people aged 50–80 who smoke or have smoked for at least 20 pack-years; this recommendation does not use the 15-year post-quit limit, which broadens the group for discussion of screening.[47]

Situation	What to do
Cough lasting more than a few weeks	See a doctor
Blood in sputum	Urgent medical assessment
Pneumonia doesn't go away	Re-visualization and search for the cause
Shortness of breath is increasing	Checking the lungs and heart
Weight loss	Exclude tumor and systemic causes
Long smoking history	Discuss low-dose computed tomography

Diagnostics

The first step is a clinical assessment. The doctor will determine smoking status, occupational exposure, exposure to radon or asbestos, family history, duration of cough, hemoptysis, shortness of breath, pain, fever, weight loss, history of pneumonia, and previous imaging studies. [48]

The second step is imaging. Typically, a chest X-ray or CT scan is the first step, but if a diffuse process is suspected, CT provides more information: it shows infiltrates, nodules, consolidations, thickening of the interlobular septa, lymph nodes, pleural effusion, and signs of spread. [49]

The third step is tissue collection. If cancer is suspected, tissue samples are needed for histological and molecular testing: bronchoscopy with biopsy, endobronchial ultrasound with lymph node puncture, transthoracic needle aspiration under computed tomography guidance, pleural biopsy, pleural fluid puncture, or surgical biopsy. [50]

The fourth step is staging. This involves computed tomography of the chest and upper abdomen, positron emission tomography combined with computed tomography, magnetic resonance imaging of the brain when indicated, and morphological confirmation of suspicious lymph nodes or metastases. [51]

The fifth step is molecular testing. In non-small cell cancer, especially non-squamous cell tumors and advanced stages, it is important to look for mutations and rearrangements that determine targeted therapy, as well as to evaluate programmed death ligand 1 to decide on immunotherapy. [52]

Diagnostic stage	What does it give?
Questioning and inspection	Assess risk and warning signs
Computed tomography	Shows the nature and extent of the lesion
Bronchoscopy	Allows you to examine the bronchi and take tissue
Needle biopsy	Confirms the diagnosis in peripheral lesions
Positron emission tomography	Helps stage the disease
Magnetic resonance imaging of the brain	Searches for brain metastases
Molecular testing	Selects targeted and immune therapy

Differential diagnosis

Diffuse lung cancer is primarily distinguished from pneumonia. If the infiltrate on CT scan does not resolve after adequate treatment, if the changes spread, if there is no convincing microbiological confirmation of infection, or if symptoms persist, pneumonia-like adenocarcinoma should be considered and a biopsy performed. [53]

The second important diagnosis is tuberculosis and non-tuberculous mycobacterial infections. These can cause cough, weight loss, weakness, hemoptysis, infiltrates, and lesions in the lungs, so microbiological diagnostics are required, not just a visual assessment of the X-ray. [54]

The third group is interstitial lung diseases. Fibrosis, organizing pneumonia, hypersensitivity pneumonitis, sarcoidosis, and drug-induced lung injury may appear as a bilateral diffuse process, but are treated fundamentally differently. [55]

The fourth group is metastases to the lungs from another organ. Multiple foci or lymphangitic carcinomatosis can be a manifestation of breast, stomach, intestinal, kidney, pancreatic, or other tumors, so it is important to determine whether it is primary lung cancer. [56]

The fifth group includes non-oncologic causes of dyspnea and infiltrates: heart failure with pulmonary edema, pulmonary embolism, alveolar hemorrhage, vasculitis, and drug toxicity. Therefore, a competent diagnosis is not limited to oncology, but rather compares images, tests, symptoms, biopsy, and progression. [57]

Disease	Why does it look like this?	How to distinguish
Pneumonia	Infiltrate, cough, fever	Dynamics after treatment, cultures, biopsy
Tuberculosis	Cough, weight loss, lesions, hemoptysis	Microbiological tests
Interstitial lung diseases	Bilateral changes and dyspnea	High-resolution computed tomography, biopsy as indicated
Metastasis from another tumor	Multiple foci	Primary tumor detection and immunohistochemistry
Cardiac pulmonary edema	Dyspnea and diffuse changes	Echocardiography, natriuretic peptides, treatment response
Pulmonary hemorrhage	Infiltrates and blood	Bronchoscopy, immunological tests

Treatment

Treatment begins with an accurate diagnosis, because "diffuse lung cancer" alone does not dictate therapy. It is necessary to know the histological type, stage, extent, patient functional status, severity of respiratory failure, presence of metastases, and the tumor's molecular profile. Without this information, it is easy to make mistakes: for example, pneumonia-like adenocarcinoma, small cell carcinoma, and metastases from another organ all have different treatments. [58]

If the tumor is localized and technically resectable, surgery may be the mainstay of treatment. For early-stage non-small cell lung cancer, anatomical resection of a lung lobe or other extensive surgery with lymph node assessment is performed, and in patients with high surgical risk, stereotactic radiation therapy is considered. [59]

For locally advanced non-small cell lung cancer, treatment often combines drug therapy, radiation therapy, and sometimes surgery. If the tumor is inoperable, concurrent chemoradiation therapy is used, followed by maintenance immunotherapy in suitable patients; this strategy has become an important standard for some patients with stage 3 disease. [60]

In advanced non-small cell lung cancer with no identified drug target, the choice often revolves around immunotherapy, chemotherapy, and their combinations. The decision depends on programmed death ligand 1 expression, histological type, disease progression, symptoms, contraindications to immunotherapy, and the patient's overall health. [61]

If a controllable molecular target is identified, targeted drugs are often preferred. Tyrosine kinase inhibitors are used for epidermal growth factor receptor alterations; specific inhibitors of this kinase are used for anaplastic lymphoma kinase rearrangements; and for alterations in ROS1, BRAF, MET, RET, NTRK, KRAS, and other pathways, appropriate drugs are selected if available and indicated. [62]

For small cell lung cancer, the approach is different. Limited stage disease is often treated with platinum- and etoposide-based chemotherapy along with chest radiation therapy, while advanced stage disease is treated with systemic therapy, including first-line immunotherapy in suitable patients. [63]

New treatments are expanding options for resistant disease. In 2025, data emerged on talarlatamab in previously treated advanced small cell lung cancer, where the drug demonstrated improved overall survival compared with standard chemotherapy; antibody-drug conjugates and new targeted agents are being developed for non-small cell lung cancer. [64]

Radiation therapy remains important not only as a radical but also as a palliative treatment. It can reduce pain from bone metastases, control hemoptysis, target brain metastases, reduce the risk of complications from chest compression, and improve quality of life. [65]

Supportive and palliative care should be initiated early, especially in diffuse and extensive disease. This includes treatment of dyspnea, pain, cough, anxiety, pleural effusion, malnutrition, thrombosis, drug side effects, and psychological stress; such care does not mean abandoning anticancer therapy, but rather complements it. [66]

Situation	Possible tactics
Early resectable tumor	Surgery, sometimes drug therapy before or after surgery
Early inoperable tumor	Stereotactic radiotherapy
Locally advanced disease	Chemoradiotherapy, immunotherapy as indicated
Molecularly targeted metastatic cancer	Targeted therapy
Metastatic cancer without a target	Immunotherapy, chemotherapy or combinations
Small cell carcinoma	Chemotherapy, radiation therapy, immunotherapy by stage
Symptomatic metastases	Palliative radiotherapy and supportive care

Prevention

The primary preventative measure is not to start smoking and to quit if you already smoke. The National Cancer Institute emphasizes that quitting smoking reduces the risk of lung cancer, and avoiding risk factors is the primary focus of prevention. [67]

Protection from secondhand smoke is also important. Laws and household measures that prevent smoking indoors, in the workplace, and around children reduce nonsmokers' exposure to carcinogens in tobacco smoke. [68]

Radon mitigation is a separate area of prevention. In regions where radon can accumulate in homes, testing of premises and technical reduction of gas concentrations when safe levels are exceeded are important. [69]

In the workplace, protection from asbestos, silica, diesel exhaust, arsenic, nickel, chromium, and other carcinogens is important. This includes engineering controls, ventilation, personal protective equipment, compliance with safety regulations, and medical supervision. [70]

Screening does not prevent cancer, but it helps detect it earlier in people at high risk. Low-dose CT scanning reduces lung cancer mortality in appropriate groups, so patients aged 50–80 with a corresponding smoking history should discuss screening with their doctor. [71]

Preventive measure	What does it give?
Quitting smoking	The largest reduction in avoidable risk
Protection from passive smoke	Reduces the effects of carcinogens
Radon testing	Reveals hidden home risk factors
Occupational safety and health	Reduces occupational carcinogenic effects
Air pollution control	Reduces long-term airway strain
Low-dose computed tomography screening	Helps detect cancer earlier in people at high risk

Forecast

The prognosis for diffuse lung cancer depends on the specific definition. Localized adenocarcinoma with the potential for radical treatment has one prognosis, while bilateral diffuse lesions, lymphangitic carcinomatosis, tumor pleural effusion, or distant metastases have a completely different prognosis. [72]

Stage remains the main prognostic factor. According to the National Cancer Institute's surveillance program, the 5-year relative survival rate for localized lung and bronchus cancer is approximately 65.5%, for regional spread - approximately 38.2%, and for distant metastases - approximately 10.5%. [73]

The molecular profile of a tumor can significantly alter the prognosis. Patients with certain mutations or rearrangements can receive targeted drugs, which often provide superior and longer-lasting disease control compared to conventional chemotherapy, although resistance to treatment over time remains a serious problem. [74]

The patient's overall condition is also very important. Age alone is not the only criterion, but severe respiratory failure, severe cardiovascular disease, weight loss, poor exercise tolerance, and comorbidities may limit treatment options. [75]

In diffuse pneumonia-like presentations, the prognosis often worsens due to delayed diagnosis. When the tumor is treated as an infection for a long time, the time to biopsy and initiation of appropriate therapy increases, so persistent "pneumonia" always requires follow-up imaging and diagnostic revision. [76]

Factor	How does it affect the prognosis?
Stage	The strongest prognostic factor
Histological type	Determines aggressiveness and treatment
Molecular targets	May pave the way for targeted therapy
General condition	Affects the tolerability of treatment
Respiratory failure	Complicates therapy
Speed of diagnosis	Particularly important in pneumonia-like forms
Response to first line treatment	It greatly influences further tactics.

Frequently asked questions

Is diffuse lung cancer a distinct type of cancer?
No. It's generally a descriptive term that refers to a widespread, scattered, infiltrative, or pneumonia-like pattern of lung disease. A definitive diagnosis should include the histologic type, stage, and molecular features of the tumor. [77]

Why is diffuse lung cancer confused with pneumonia?
Because pneumonia-like adenocarcinoma can cause lumps in the lung tissue, cough, sputum, shortness of breath, and sometimes signs of inflammation. If changes persist after treatment or return, a CT scan and biopsy are needed. [78]

Can a diagnosis be made with a CT scan alone?
Usually not. CT scans can suggest cancer and show its spread, but definitive confirmation requires tissue or cytology, and molecular testing is often needed to determine treatment. [79]

What blood tests indicate lung cancer?
Routine blood tests do not confirm lung cancer. They help assess anemia, inflammation, liver and kidney function, calcium, general condition, and treatment safety, but the diagnosis is confirmed by imaging, biopsy, and pathological examination. [80]

Is diffuse lung cancer always incurable?
Not always, because the term "diffuse" is used differently. However, bilateral lesions, tumor effusion, lymphangitic carcinomatosis, or distant metastases often indicate an advanced stage, at which point the goal of treatment is often long-term disease control and improved quality of life. [81]

What are the most important modern drugs?
Immunotherapy and targeted therapy have become key. In the presence of specific molecular changes, drugs targeting a specific oncogenic pathway are used, and in the absence of such targets, immunotherapy, chemotherapy, or a combination of both are often used. [82]

Should all patients undergo molecular testing?
For advanced non-small cell lung cancer, molecular testing is usually a mandatory part of modern diagnostics, especially for adenocarcinoma. It helps identify treatments that may be more effective than standard chemotherapy for a particular patient. [83]

Does screening help detect diffuse lung cancer earlier?
Low-dose CT screening helps detect lung cancer earlier in high-risk individuals, but it does not guarantee detection of all forms and is not intended for people without relevant risk factors. Screening criteria should be discussed with a doctor. [84]

Key points from experts

Harold Varmus, a Nobel Prize-winning physician and former director of the US National Cancer Institute, and Avrum Spira, a pulmonologist and researcher in early lung cancer diagnosis. Their shared expert thesis in modern pulmonary oncology: lung cancer must be detected earlier and more accurately, because the stage at diagnosis dramatically impacts survival, and screening and molecular diagnostics are changing the treatment trajectory. [85]

William D. Travis, a pathologist, is one of the World Health Organization's leading experts on the classification of lung tumors. The key thesis of his field is that the diagnosis of lung cancer should be based on morphology, immunohistochemistry, and molecular data, because only in this way can adenocarcinoma, squamous cell carcinoma, neuroendocrine tumors, and other types of tumors be accurately differentiated. [86]

Frank C. Detterbeck, MD, a thoracic surgeon and a member of the International Association for the Study of Lung Cancer staging project, said: "Key point: Diffuse pneumonia-like adenocarcinoma and multiple tumor foci require special staging logic because they cannot always be assessed as a single nodule." [87]

Mariano Provencio and Enriqueta Felip, oncologists and participants in European expert approaches to lung cancer treatment, say: "The key message of modern treatment is that in advanced non-small cell lung cancer, first-line therapy should take into account not only the stage but also molecular targets, programmed death ligand 1 expression, histology, and the patient's overall condition." [88]

Experts from the U.S. Preventive Services Task Force and the American Cancer Society. Key message: Annual low-dose CT scanning in high-risk individuals reduces lung cancer mortality, so screening should be discussed with patients aged 50–80 years with a sufficient smoking history. [89]

Expert opinion	Practical significance
"Diffuse" does not replace a morphological diagnosis	A biopsy is needed
The stage dramatically affects the prognosis.	A comprehensive prevalence assessment is needed
Molecular testing is changing treatment.	Systemic therapy should not be initiated blindly if there is time for testing
Pneumonia-like adenocarcinoma masquerades as infection	Caution is needed in persistent pneumonia
Screening reduces mortality in high-risk groups	Low-dose CT scan is important before symptoms appear

Result

Diffuse lung cancer is a descriptive term, not a distinct tumor type. It may include pneumonia-like adenocarcinoma, multifocal non-small cell lung cancer, small cell lung cancer, lymphangitic carcinomatosis, or metastases to the lungs from another organ. [90]

The primary diagnostic goal is to confirm cancer with tissue and determine its type. Computed tomography (CT) scans show the extent of the disease, but treatment is determined based on the results of biopsy, histology, immunohistochemistry, molecular testing, and staging. [91]

A particularly dangerous situation is when a diffuse tumor is mistaken for pneumonia for a long time. If the infiltrate does not resolve, symptoms persist, "pneumonia" recur, or the disease behaves atypically, the diagnosis must be re-evaluated and a biopsy considered. [92]

Treatment may include surgery, radiation therapy, chemotherapy, immunotherapy, targeted therapy, new antibody-drug conjugates, and palliative care. There is no universal regimen: the plan depends on the stage, tumor type, molecular features, and the patient's condition. [93]

Prevention revolves around stopping smoking, protection from passive smoke, radon and occupational carcinogens, and early detection in high-risk individuals is possible through annual low-dose CT scanning.[94]