A 52-year-old woman who is a nonsmoker has a 3-cm right inguinal lymph node.Biopsy specimen shows a poorly differentiated malignancy that is difficult to characterize by light microscopy. The biopsy specimen is negative for leukocyte common antigen, cytokeratin, and estrogen receptors. Which of the following additional tests would best establish the source of this tumor?

Question

Quizplus · Accepted Answer

Stain for S-100 is the best choice because the tumor's negative staining for leukocyte common antigen, cytokeratin, and estrogen receptors, along with its location and the patient's demographic, suggests a melanoma, which is best identified by S-100 protein staining.

A 52-Year-Old Woman Who Is a Nonsmoker Has a 3-Cm