Case Report: Pazopanib Treatment Response in a Patient with Metastatic Pleomorphic Dermal Sarcoma (Atypical Fibroxanthoma) with Circulating Tumor Cell-Derived Colonies as a Predictive Marker

Atypical fibroxanthomas (AFX) are rare skin tumors. These generally are superficial tumors, usually 376 colonies. The patient could not tolerate additional chemotherapy. She was therefore treated with the oral targeted agent pazopanib. The patient developed a dramatic biopsy-confirmed complete response. After 11 months of pazopanib treatment, a repeat CTC-derived culture sample grew only 8 colonies/10 ml blood. The complete response to pazopanib is still ongoing at over 41 months. To our knowledge, this is the first demonstration of clinical complete response of a PDS tumor following targeted therapy. An additional novel feature was the demonstration that CTC-derived colonies could be grown from the blood of a PDS patient. The number of colonies appeared to correlate with the clinical treatment response and seemed to function as a potential prognostic marker.