Histopathological types of lung cancer

The histopathological classification of lung cancer is now divided into two major categories: non-small cell lung cancer and small cell lung cancer.

1. Non-small cell carcinoma According to WHO standards, lung cancer can be divided into squamous cell carcinoma, adenocarcinoma, large cell carcinoma, adenosquamous carcinoma, bronchial adenocarcinoma, and non-small cell carcinoma.

(1) Squamous cell lung cancer: It accounts for 30% of the total number of lung cancer patients. It is a malignant epithelial tumor with keratinization and intercellular bridges. Squamous cell carcinoma is more common in the central type, which is mostly composed of tumor tissue and large pieces of necrosis and cavitation. Bronchial irritation symptoms appear early, and the positive rate of fiberoptic bronchoscopy is high. The diagnosis is based on the discovery of desmosomes and tension fibrils in the cytoplasm under light microscopy. It is more common in male smokers, develops slowly, has a low rate of distant metastasis, and has a high long-term survival rate after surgery.

(2) Adenocarcinoma: It accounts for 50% of all histological types of lung cancer and is currently the most common type of lung cancer. The typical type is mainly glandular structure, while poorly differentiated ones may lack acinar and papillary structures. Peripheral type is more common and occurs more frequently in women. Hematogenous metastasis is common. Once the pleura is affected, it is easy to metastasize to the mediastinal lymph nodes through the lymphatic system. Bronchioloalveolar cell carcinoma is a special type of adenocarcinoma. It has no obvious glandular structure and its morphology is similar to that of alveolar type II cells. It mainly manifests in two distinct gross morphologies: isolated nodules confined to the lung segments and diffuse infiltrative changes throughout the lungs.

(3) Undifferentiated large cell carcinoma: This type of lung cancer has no obvious features under light microscopy, and there is no glandular or squamous differentiation. The diagnosis can only be established after excluding other types of lung cancer. The main difference from small cell lung cancer under light microscopy is that the cytoplasm is rich, the cell boundaries are clear, and the cells are arranged tightly and uniformly. Under electron microscopy, differentiation of adenocarcinoma, squamous cell carcinoma and small cell carcinoma can often be found. The origin of large cell carcinoma has nothing to do with the bronchi, and it often occurs in the terminal bronchi and subsegmental areas. It invades the parenchyma and metastasizes in the early stage. Occasionally, it invades the surrounding lung tissue and appears as a pseudocapsule on CT.

(4) Adenosquamous carcinoma: rare, characterized by the presence of two cytological components in the same cancer tissue, and therefore also has the biological characteristics of two cells, with a poor prognosis.

(5) Bronchial gland carcinoma: A group of primary lung and bronchial tumors originating from the mucous glands and glandular epithelial cells of the bronchial submucosal membrane. The incidence is low, accounting for only about 2%. The tumor grows slowly, with clear boundaries when observed with the naked eye, but it often invades adjacent tissues and can metastasize to distant sites. Local recurrence is likely if the excision is not thorough, so it should be classified as a low-grade malignant tumor. Bronchial adenomas often occur in larger bronchi, are rich in tumor blood vessels, and occur at a young age, mostly in women.

2. Small cell lung cancer is composed of uniform small cells, typically oat-like. Electron microscopy reveals argyrophilic granules and neuroendocrine granules in the cytoplasm, which can confirm the diagnosis. Generally, necrosis and cavitation are not formed. It is prone to occur in the submucosal layer of the lobar bronchus. It is the most malignant, poorly differentiated, and grows fast. It has lymphatic and hematogenous metastases in the early stage. It is sensitive to radiotherapy and chemotherapy, but the prognosis is poor. The prognosis of typical small cell lung cancer is better than that of atypical small cell lung cancer.