Primary cutaneous carcinomas rarely show heterologous malignant mesenchymal differentiation.

References

 Sarcomatoid basal cell carcinoma—predilection for osteosarcomatous differentiation: a series of 11 cases. Mc Menamin ME, Goh SG, Poblet E, Gostelow BE, Robson A, Calonje E. Am J Surg Pathol. 2006 Oct;30(10):1299-308. PMID: 17001162