Tumors of the lung :
A variety of benign and malignant tumors may arise in the lung, but the vast majority (90% to 95%) are carcinomas.CARCINOMAS
Lung cancer is currently the most frequently diagnosed major cancer in the world and the most common cause of cancer mortality worldwide. This is largely due to the carcinogenic effects of cigarette smoke. Over the coming decades, changes in smoking habits as the use of filters and light tobacco cigarettes increased the incidence of distal bronchiolar and alveolar carcinogenesis at the expense of proximal squamous cell carcinoma. The incidence rate is declining significantly in men, while rates for women continued to increase. Cancer of the lung occurs most often between ages 40 and 70 years, with a peak incidence in the fifties or sixties. the 5-year survival rate for all stages combined is only 15%.
Etiology and Pathogenesis:
Carcinomas of the lung, similar to cancer at other sites, arise by a stepwise accumulation of genetic abnormalities that transform benign bronchial epithelium to neoplastic tissue. Unlike many other cancers, the major environmental insult that inflicts genetic damage is known which is cigarette smoking .
Perinvasive lesions of lung cancer:
squamous metaplasia which is caused from cigarettes smocking can be developed to dysplasia in bronchial lining epithelium with it's grading as mild, moderate and severe dysplasia or carcinoma in situ as precursor for development of invasive SCC, while atypical adenomatous hyperplasia in lower bronchial and epithelium lined alveoli can cause adenocarcinoma .NEW WHO CLASSIFICATION OF BRONCHOGENIC CARCINOMA.
The bronchogenic carcinoma classified by WHO at 2015 asI- Small cell carcinoma which is show 20% of tumors.
II- Non small cell carcinoma show 80% of tumor. (NSCLC)
These include:
1- Adenocarcinoma .
2-squamous cell carcinoma.
3- Large cell neuroendocrine tumor.
4-Large cell carcinoma.
III-metastatic carcinoma.
Squamous Cell Carcinoma. Squamous cell carcinoma is most commonly found in men and is closely correlated with a smoking history. Histologically, this tumor is characterized by the presence of keratinization and/or intercellular bridges. Keratinization may take the form of squamous pearls or individual cells with markedly eosinophilic dense cytoplasm. These features are prominent in the well- differentiated tumors, are easily seen but not extensive in moderately differentiated tumors, and are focally seen in poorly differentiated tumors. Mitotic activity is higher in poorly differentiated tumors.
Adenocarcinoma This is a malignant tumor with glandular differentiation or mucin production by the tumor cells. Adenocarcinoma various growth patterns, either pure or, more mixed. These patterns are acinar, papillary, bronchioaloalveolar, and solid with mucin formation. Adenocarcinoma is the most common type of cancer in women and nonsmokers. As compare squamous cell cancers, the lesions are usually peripherally located, and tend to be smaller They vary histologically from well-differentiated tumors with obvious glandular elements to papillary tumor.
Small Cell Carcinoma. This highly malignant tumor has a distinctive cell type. The epithelial cells are small, with scant cytoplasm, ill-defined cell borders, finely granular nuclear chromatin (salt and pepper pattern), and absent or inconspicuous nucleoli. The cells are round, oval, and spindle- shaped, and nuclear molding is prominent. There is no absolute size for the tumor cells, but in general, they are smaller than small resting lymphocytes. The mitotic count is high. The cells grow in clusters that exhibit neither glandular nor squamous organization. Necrosis is common and often extensive ,grading is inappropriate, since all small cell carcinomas are high grade.
Small cell carcinomas have a strong relations to cigarette smoking; only about 1% occur in nonsmokers. They occur both in major bronchi and in periphery of the lung. There is no carcinoma in situ phase. They are the most invasive type of lung tumors, metastasize widely, and it is incurable by surgical means.
Large Cell Carcinoma
This is an undiffererntiated. malignant epithelial tumor that lacks the cytological features of small cell carcinoma and glandular or squamous differentiation. The cells typically have large hyperchromatic nuclei, prominent nucleoli, and a moderate amount of cytoplasm. Large cell carcinomas probably represent squamous cell carcinomas and adenocarcinoma that are so undifferentiated that they no longer be recognized by light microscopy.METASTATIC TUMORS The lung is the most common site of metastatic neoplasm. Both carcinomas and sarcomas arising anywhere in the body may spread to the lungs via the blood or lymphatic or by direct continuity. Growth of contiguous tumors into the lungs
Pleura
PLEURAL TUMORS
The pleura may be involved by primary or secondary tumors. Secondary metastatic involvement is far more common than are primary tumors. The most frequent metastatic malignancies arise from primary neoplasms of the lung and breast. In addition to these cancers, malignancy from any organ of the body may spread to the pleural spaces.
Malignant Mesothelioma
Malignant mesotheliomas in the thorax arise from either the visceral or the parietal pleura. Though uncommon, they have assumed great importance in the past few years because of their increased incidence among people with heavy exposure to asbestos for asbestos workers (particularly those who are also smokers), the risk of dying of lung carcinoma far exceeds that of developing mesothelioma.
Morphology. Malignant mesothelioma is a diffuse lesion that spreads widely in the pleural space and is usually associated with extensive pleural effusion and direct invasion of thoracic structures. The affected lung becomes ensheathed by a thick layer of soft, gelatinous, grayish pink tumor tissue .
Microscopically, malignant mesotheliomas may be epithelioid (60%), sarcomatoid (20%), or mixed (20%). This is in keeping with the fact that mesothelial cells have the potential to develop as epithelium-like cells or mesenchymal stromal cells.
Mesotheliomas also arise in the peritoneum, pericardium.