Tumor structure and epidemiology
Among all neoplasms of the respiratory system, the vast majority account for lung cancer (from 90 to 95%). Carcinoids (about 5%) and tumors of mesenchymal origin (from 2 to 5%) are significantly less common.
In global statistics, the incidence exceeds 1 million new cases annually, which accounts for more than 10% of all newly diagnosed malignant tumors. Geographically, the disease is distributed unevenly: about 58% of all clinical cases are registered in developed countries.
European statistics deserve special attention, as this pathology firmly occupies the first place in both incidence and mortality rates. In terms of gender breakdown, the picture is as follows:
- Men: lung cancer accounts for 21% of all diagnosed tumors and causes 29% of mortality (overall, it accounts for about 30% of all cancer deaths in men).
- Women: the proportion in the tumor structure is 5%, and mortality is 9%. It is important to note the alarming trend: over the past twenty years, incidence and mortality among women have increased significantly. To date, mortality rates from this pathology in women have already exceeded those for breast cancer.
Terminology, prognosis, and social significance
In specialized medical literature, the synonym "bronchogenic carcinoma" (or bronchogenic cancer) is often used. This term is not accidental: it clearly indicates the histogenesis of the neoplasm, emphasizing its origin from the epithelial lining of the bronchi and bronchioles.
The social significance of the problem is colossal. It is the most common malignant tumor and the leading cause of cancer death in industrially developed countries.
The prognosis for patients remains extremely unfavorable, which is why lung cancer is considered the most fatal malignant tumor. The main problem lies in late diagnosis: in 75% of cases, the disease is detected at advanced stages when radical surgical treatment is no longer possible. As a result, survival rates remain extremely low, and even the use of complex modern therapy cannot fundamentally change the situation.
Conditions of development and risk factors
The process of malignant transformation (malignization) has been confirmed both in experimental conditions and in clinical practice. However, specific background conditions are required for its initiation and the concentration of carcinogenic substances.
The key factors contributing to tumor development are chronic inflammation and pneumosclerosis. Their mechanism of action is that in damaged tissues, there is a disruption of immunological control over mutated cells, as well as a failure of normal intercellular regulatory interactions.
Of greatest clinical significance as precancerous states are:
- Decompensated chronic inflammation and areas of pneumosclerosis forming in tuberculosis.
- Idiopathic fibrosing alveolitis (IFA).
- Scar changes in lung tissue remaining after a previous pulmonary infarction.
- Chronic inflammation localized around foreign bodies (in pathological anatomy, this condition is often called "scar cancer").
Morphogenesis and molecular basis
The pathogenesis of the tumor represents a complex chain of morphological changes. In foci of chronic inflammation and zones of pneumosclerosis, foci of proliferation of the bronchial, bronchiolar, and alveolar epithelium arise primarily. The cellular composition of these foci is very diverse: basal, ciliated, and mucous cells, as well as Clara cells and type II alveocytes, are detected in them.
With further progression of the pathological process, the following changes develop:
- Metaplasia and dysplasia of the bronchial and bronchiolar epithelium.
- Formation of adenomatosis foci accompanied by pronounced epithelial cell atypia.
- Atypical epithelial hyperplasia localized in specific oval and slit-like structures within zones of pneumosclerosis.
The described changes are of critical importance for the development of cancer from small bronchi and bronchioles. At the same time, controversial points remain in the scientific community, in particular, the possibility of cancer arising directly from transformed type II alveocytes is actively debated. It is important to remember that the variant of carcinoma development de novo is also possible — that is, without any preceding precancerous changes.
The molecular basis of pathogenesis is determined by a complex combination of morphological and molecular-genetic features. Key aspects here include the pathology of apoptosis processes and the determination of specific biomolecular and histogenetic markers, which include various genes, proteins, and hormones.
Briefly: answers to topical questions
What histological types of lung cancer are distinguished according to the international classification?
According to the WHO histological classification (2004), eight groups are distinguished:
- Squamous cell carcinoma — papillary, clear cell, small cell, and basaloid.
- Small cell carcinoma — combined carcinoma.
- Adenocarcinoma — mixed subtype, acinar, papillary, bronchioloalveolar (non-mucinous, mucinous, mixed), solid adenocarcinoma with mucin production.
- Adenosquamous carcinoma.
- Sarcomatoid carcinoma — pleomorphic, spindle cell, giant cell, carcinosarcoma, blastoma.
- Carcinoid tumors — typical and atypical carcinoids.
- Salivary gland tumors — mucoepidermoid, adenoid cystic, epithelial-myoepithelial carcinoma.
- Precancerous (pre-invasive) lesions — squamous cell carcinoma in situ, atypical adenomatous hyperplasia, diffuse idiopathic pulmonary neuroendocrine cell hyperplasia.
Into what types is lung cancer divided depending on localization relative to the bronchial tree?
Depending on localization, three clinical and anatomical types of lung cancer are distinguished:
- Central (root) cancer — originates from the epithelium of large bronchi: main, lobar, segmental, and subsegmental.
- Peripheral cancer — originates from the epithelium of smaller bronchi, bronchioles, and possibly alveoli.
- Massive (mixed) cancer — a late stage of development of central or peripheral cancer, when the tumor reaches large sizes and the initial localization cannot be established.
What macroscopic growth forms are characteristic of central lung cancer?
Central (root) lung cancer is characterized by the following macroscopic forms:
- Polypoid.
- Nodular.
- Branched.
- Nodular-branched.
By the nature of growth, exophytic (endobronchial), endophytic (exobronchial, peribronchial), branched, and mixed growth are distinguished.
What specific genes and mutations serve as the main molecular-genetic markers of lung cancer?
The main molecular-genetic markers of non-small cell lung cancer are driver mutations and immune response markers.
- Gene mutations — activating mutations in EGFR (exons 18–21) and BRAF genes.
- Gene translocations — rearrangements (translocations) of ALK and ROS1 genes.
- Immunohistochemical markers — expression of the PD-L1 protein on tumor cells.
These markers are determined to select the tactics of targeted therapy and immunotherapy, especially in inoperable non-squamous cell carcinoma.
What are the main pathways and typical target organs of hematogenous metastasis in lung cancer?
Hematogenous metastasis of lung cancer predominantly occurs in the late stages of the disease. Typical target organs for hematogenous metastases are:
- Liver
- Bones
- Adrenal glands
- Brain
This pathway of spread is particularly characteristic of peripheral lung cancer, and distant metastases are frequently the cause of patient mortality.
Which lymph node groups are involved in regional lymphogenous metastasis in lung cancer?
Lymphogenous metastasis of lung cancer predominantly occurs in early stages. The first metastases appear in regional lymph nodes: peribronchial and bifurcation nodes in central (root) cancer. In late stages, paratracheal, mediastinal, and cervical lymph nodes are affected.
To memorize the main background processes (precancerous conditions), use the acronym TIRI: Tuberculosis (pneumosclerosis), Idiopathic fibrosing alveolitis (IFA), Rscars (following myocardial infarction — note: post-infarct pulmonary scar), Intrusions (foreign bodies and surrounding inflammation — "scar cancer").
Class and exam questions
Why is lung cancer often referred to as bronchogenic carcinoma?
This term emphasizes the histogenesis of the tumor — it originates from the epithelial lining of the bronchi and bronchioles.
Do precancerous changes always precede lung cancer?
No, not always. Although the tumor frequently develops against a background of dysplasia and metaplasia within foci of pneumosclerosis, its emergence de novo — without a preceding background — has been proven.
What is the prognosis for lung cancer and what factors determine it?
The prognosis is extremely unfavorable. This is due to the fact that about 75% of cases are diagnosed at late stages, when surgical treatment is no longer applicable and conservative therapy has low efficacy.
What is the mechanism of action of background diseases in lung cancer?
Chronic inflammation and pneumosclerosis disrupt immunological control over mutated cells and impair intercellular regulatory interactions, which promotes malignant transformation.
What else to study on this topic
- Histological classification of lung cancer (squamous cell, adenocarcinoma, small cell, etc.)
- Features of bronchogenic carcinoma metastasis
- Pathology of apoptosis in malignant lung neoplasms
- Biomolecular and histogenetic markers of lung cancer (genes, proteins, hormones)
- Differential diagnosis with carcinoids and mesenchymal tumors
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