6 - Squamous, large cell, and sarcomatoid carcinomas

Summary

Clinical features

Squamous cell carcinoma, accounting for approximately 20% of lung cancers, is the second most common type of non-small cell carcinoma, the first being adenocarcinoma. Clinically, squamous cell carcinomas have a better 5-year survival rate than adenocarcinomas at the same stage. More than 90% of squamous cell carcinomas occur in cigarette smokers. It is important to diagnose accurately squamous cell carcinoma, which is associated with a high risk of bleeding to angiogenesis inhibitor, bevacizumab (Avastin). Furthermore, typically it does not respond as well to premetrexed as do adenocarcinomas.

About one-third of squamous cell carcinomas arise at the periphery while two-thirds are centrally located, arising from main stem, lobar, or segmental bronchi. Central tumors grow along the bronchial mucosa toward the hilum. Squamous dysplasia and in situ carcinoma develop in the bronchial mucosa of cigarette smokers and of individuals exposed to environmental carcinogens. They arise from segmental bronchi in single or often multiple locations, extending peripherally to the subsegmental bronchi, and eventually to the lobar bronchi. Peripheral tumors occur in older patients and have a better survival rate than central ones. These tumors have three growth patterns: (1) pushing – lobules of squamous cell carcinoma with well-defined borders; (2) infiltrative – nests of squamous cell carcinoma infiltrating alveolar septa; and (3) alveolar filling – cohesive groups of squamous cell carcinoma enclosed by intact alveolar septa. It is suggested that the alveolar filling type, which represents about 5%, may be the earliest stage “incipient” peripheral squamous cell carcinoma.