Lung cancers are usually divided into two main groups that account for about 95% of all cases.
The division into groups is based on the type of cells that make up the cancer.
The two main types of lung cancer are characterized by the cell size of the tumor when viewed under the microscope. They are called small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). NSCLC includes several subtypes of tumors.
SCLCs are less common, but they grow more quickly and are more likely to metastasize than NSCLCs. Often, SCLCs have already spread to other parts of the body when the cancer is diagnosed.
About 5% of lung cancers are of rare cell types, including carcinoid tumor, lymphoma, and others.
The specific types of primary lung cancers are as follows:
Adenocarcinoma (an NSCLC) is the most common type of lung cancer, making up 30%-40% of all cases. A subtype of adenocarcinoma is called bronchoalveolar cell carcinoma, which creates a pneumonia-like appearance on chest x-rays.
Squamous cell carcinoma (an NSCLC) is the second most common type of lung cancer, making up about 30% of all lung cancers.
Large cell cancer (another NSCLC) makes up 10% of all cases.
SCLC makes up 20% of all cases.
Carcinoid tumors account for 1% of all cases.
DIFFERENCES B/W -small cell and non small cell types-
SCLC(small cell) exhibits
2.with rapid growth,
3.early spread to distant sites,
4.exquisite sensitivity to chemotherapy and radiation, and
5.frequent association with distinct paraneoplastic syndromes.
6.Surgery usually plays no role in its management, except in rare situations (<5%>
- Cigarette smoking is the most important cause of lung cancer
- Passive smoking, or secondhand smoke
- Air pollution
- Asbestos exposure:. Another cancer known as mesothelioma (a type of cancer of the pleura or of the lining of the abdominal cavity called the peritoneum) is also strongly associated with exposure to asbestos.
- Lung diseases, such as tuberculosis (TB) and chronic obstructive pulmonary disease (COPD), also create a risk for lung cancer
- Radon exposure poses another risk.
Histologic Findings: The World Health Organization classification of lung cancer is widely accepted. NSCLC includes squamous cell carcinoma, adenocarcinoma, and large cell carcinoma. Sometimes, lung cancers can exhibit 2 or more histologic patterns.
Adenocarcinoma appears to be increasing in incidence, especially in women, compared with squamous cell carcinoma, which was previously the most common type of NSCLC.
Squamous cell carcinoma has a distinct dose-response relationship to tobacco smoking and usually develops in proximal airways, progressing through stages of squamous metaplasia to carcinoma in situ. Well-differentiated squamous cell carcinomas contain keratin pearls, while poorly differentiated squamous cell carcinomas may stain positive for keratin. Microscopic examination reveals cells with large, irregular nuclei and coarse nuclear chromatin with large nucleoli. Cells are arranged in sheets, and the presence of intercellular bridging is diagnostic.
Adenocarcinoma is the most common type of NSCLC. Histologically, adenocarcinomas form glands and produce mucin. Mucin production can be identified with mucicarmine or periodic acid-Schiff staining. The World Health Organization classification of lung cancer divides adenocarcinomas into (1) acinar, (2) papillary, (3) bronchoalveolar, and (4) mucus-secreting. Bronchoalveolar carcinoma is a distinct clinicopathologic entity that appears to arise from type II pneumocytes and may manifest as a solitary peripheral nodule, multifocal disease, or a pneumonic form, which can spread rapidly from one lobe to another. Stage for stage, adenocarcinomas are associated with worse prognoses than squamous cell carcinomas, with the exception of T1 N0 M0 tumors.
Large cell carcinoma is the least common of all NSCLCs. It is composed of large cells with prominent nucleoli, and no mucin production or intercellular bridging is identified. Many tumors previously diagnosed as large cell carcinomas are identified as poorly differentiated adenocarcinomas or squamous cell carcinomas after advanced immunohistochemical staining, electron microscopy, and monoclonal antibody studies. A variant of large cell carcinoma has been identified; it contains neuroendocrine features and is called large cell neuroendocrine carcinoma. Large cell neuroendocrine carcinomas are associated with a worse prognosis than large cell carcinomas.
SCLC typically are centrally located, arising in peribronchial locations. They are thought to arise from Kulchitsky cells.
The tumor is composed of sheets of small, round cells with dark nuclei, scant cytoplasm, fine granular nuclear chromatin, and indistinct nucleoli.
Crush artifact leading to nuclear molding is a common finding, but it is not considered diagnostic.
Very high rates of cell division are observed, and necrosis, sometimes extensive, may be seen. Because of the central location, the cells exfoliate in sputum and bronchial washings.
Neurosecretory granules can be identified on electron microscopy, and the neuroendocrine nature of the neoplasm is suggested by its frequent association with paraneoplastic syndromes caused by peptide hormones.
Immunohistochemical stains for chromogranin, neuron-specific enolase, and synaptophysin usually are positive.
thats for today more about its treatment tommorrow,bye