Extrapulmonary Small Cell Carcinoma: Imaging Features with Radiologic-Pathologic Correlation

Extrapulmonary small cell carcinoma (EPSCC) refers to small cell carcinoma arising outside of the lungs. EPSCC is a rare aggressive neoplasm, representing a minority of all small cell carcinomas. Despite its uncommon occurrence, EPSCC has been described in nearly every organ, most commonly in the gastrointestinal and genitourinary systems. As such, it is important for radiologists to be aware of the entity. Although imaging is neither sensitive nor specific for EPSCC, it plays an important role by helping exclude metastases from a primary pulmonary tumor, establish tumor staging, and assess response to therapy. EPSCC is diagnosed by demonstrating pathologic features of small cell carcinoma in an extrapulmonary site. There are two ways to stage EPSCC. One method uses the Veterans Administration Lung Study Group system developed for small cell lung cancer that allocates patients into limited or extensive disease categories. The second approach is the American Joint Committee on Cancer tumor-node-metastasis system applied to other tumor subtypes arising from the same organ. Because of its rare and varied manifestations, the most effective treatment for EPSCC has not been established. Current management recommendations are derived from retrospective studies and single-institution experiences or are extrapolated from small cell lung cancer data. Regardless of therapy, overall survival rates are poor, with 5-year survival rates around 13%. To help radiologists increase their familiarity with EPSCC, this article provides (a) a background for EPSCC based on the literature and (b) a pictorial review of EPSCC in multiple organs, with radiologic-pathologic correlation. (C)RSNA, 2015