Update of the S1‐guideline atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS)

Summary Atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS) are rare cutaneous neoplasms representing histomorphological, genetic as well as epigenetic variants of one disease spectrum. Both tumors manifest as nonspecific, often ulcerated nodules in chronically sun‐damaged skin. AFX is a well‐demarcated, often rapidly growing tumor. PDS tumors are poorly circumscribed and characterized by a more aggressive infiltrative growth pattern. Histologically, both are composed of spindle‐shaped and epithelioid tumor cells with pleomorphic nuclei as well as atypical multinucleated tumor giant cells. Atypical mitoses are common. In contrast to AFX, PDS extends into the subcutis and shows areas of tumor necrosis and/or perineural infiltration. Due to the undifferentiated morphology of AFX/PDS, histopathologically similar tumors must be excluded by immunohistochemical analysis. The treatment of choice is microscopically controlled surgery. In cases of AFX, cure can be assumed after complete excision. When PDS tumors are surgically excised with a 2 cm margin or by microscopically controlled surgery, local recurrence rates are low. Metastases are rare and are mostly associated with very thick or incompletely excised tumors, primarily affecting the skin and lymph nodes. Distant metastases are even rarer. There is currently no approved and effective systemic therapy. Treatment with immune checkpoint inhibitors appears promising.