What histological feature distinguishes small cell lung cancer from non-small cell lung cancer?

The distinguishing histological feature of small cell lung cancer (SCLC) is the presence of small round cells with scant cytoplasm. This specific cellular morphology is a defining characteristic of SCLC, which arises from neuroendocrine cells and typically exhibits a high rate of proliferation. The cells are usually small, oval, and characterized by little cytoplasm relative to the size of the nucleus, which gives them a high nuclear-to-cytoplasmic ratio.

In contrast, non-small cell lung cancer (NSCLC) encompasses a variety of other cell types, including adenocarcinoma and squamous cell carcinoma, which exhibit different histological features such as more abundant cytoplasm and distinct cellular architecture. The other choices highlight characteristics more associated with these different types of lung cancer. For example, the presence of keratin is typical of squamous cell carcinoma, large cell type histology refers to a specific subtype within NSCLC that features larger cells, and well-differentiated squamous cells are indicative of another specific NSCLC subtype. Thus, the unique histological presentation of small round cells with scant cytoplasm firmly identifies small cell lung cancer.