Merkel cell carcinoma with sarcomatous differentiation: is it a poor prognostic factor?

Background: Poor prognostic factors in Merkel cell carcinoma include male sex, advanced stage at diagnosis, large tumor size (>5 mm), diffuse growth pattern, heavy lymphocytic infiltrate, and high mitotic rate. To date only six cases of Merkel cell carcinoma with sarcomatous or pseudosarcomatous differentiation and poor prognosis have been documented.
Methods: We present a new case of Merkel cell carcinoma with sarcomatous differentiation.
Results: The immunohistochemical staining patterns reflected the morphologic differentiation of the epithelial and sarcomatous pattern. After two months of follow-up, there were no signs of local recurrence or metastases.
Conclusion: In all cases of merkelomas with sarcomatous differentiation described to date, lymph node metastases have been found, except in the presented case. However, larger series of cases will be required to determine if sarcomatous differentiation represents another negative prognostic factor.
(© 2013 The International Society of Dermatology.)