Small Cell Carcinoma
In small cell lung carcinoma (SCLC), the tumor cells are small (usually less than 3 times the diameter of small resting lymphocytes), round, oval or spindle shaped with scant cytoplasm and ill-defined cytoplasmic borders. Nuclei are hyperchromatic with finely dispersed granular chromatin (salt and pepper appearance). Nucleoli are absent or inconspicuous. Nuclear molding is a constant finding. Mitotic activity is increased. Necrosis is usually present. SCLC is, by definition, a high-grade tumor and no further grading is necessary.
The key distinguishing features between small cell and non-small cell morphology are chromatin pattern (finely dispersed and no clumps in SCLC) and nucleoli (absent or inconspicuous in SCLC). It is not based on the presence or absence of neuroendocrine differentiation or the nuclear size.