Microscopic Features Small cell tumors form sheets of uniform cells separated by thin strands of connective tissue. Peripheral palasading of the nuclei may also be present. Occasionally rosettes may be found. Zones of necrosis are typically present in the center, and vary in size. At low power magnification the cells are very hyperchromatic appearing owing to the tightly packed small cells with scanty cytoplasm.
Individual cells vary in shape from ovoid to fusiform.
The cells of small cell carcinoma bear a superficial similarity to normal lymphocytes. However, small cell carcinoma nuclei are about twice the size of normal lymphocyte nuclei. The nuclei are generally molded to the shape of the cell and show dense homogenous chromatin and nucleoli are difficult to identify. Making the diagnosis of small cell lung cancer can be aided by the use of immunohistochemical stains for neuroendocrine features and cell products. Use of these stains aids in distinguishing this tumor from other small blue cell tumors, such as lymphoma.