Histological Classification of lung cancers
The lungs are made up of many different types of cells. The histological classification of lung tumors depend on the specific cell type that has undergone DNA modifications and consequently accumulated cells, giving birth to the tumor.
If the damage involves the cells of the bronchial epithelium lining the medium-large airways, this would be a squamous cell cancer. On the other hand, when peripheral bronchioles (smaller airways) are involved, adenocarcinoma develops, which today represent the most frequent histotype.
If the damage occurs within neuroendocrine cells, which are hormone-secreting, carcinoid tumors develop. Carcinoids can be typical, where the cell has a limited proliferative capacity (multiplying slowly) or atypical, where the tumor proliferates much faster and accompanied by areas of necrosis. If the accumulation mutations result in poor cellular differentiation and an increased speed of tumor growth, small cell lung tumors (microcytomas) or large cell neuroendocrine tumors develop. The latter two subtypes are characterized as more aggressive than carcinoid tumors and have a high potential for malignancy.
Large cell neuroendocrine tumors, squamous cell tumors and adenocarcinomas are classified under the subgroup of non-small cell lung tumors, distinguished from small cell lung tumors, which usually cannot be treated by surgery.
With the exception of adenocarcinomas, which are sometimes found in non-smokers, all other histotypes are associated almost exclusively with cigarette smoking. Furthermore, the variation in the type of filter used for cigarette production has changed the disease’s epidemiology. The formation of smaller inhaled particles, caused by the new filters, allows the inhaled smoke to reach the terminal bronchioles. Consequently, the incidence of squamous cell carcinoma has reduced, and adenocarcinoma increased.
Histological classification is one of the fundamental elements to be considered for therapy choice. The multidisciplinary team in charge of the patient, must precisely define the histology of the disease.
Today, it is no longer sufficient to know whether the disease is a small cell or non-small cell tumor, but whether it is a squamous cell carcinoma, an adenocarcinoma, or a large cell or small-cell neuroendocrine tumor.