An analysis of the use of targeted therapies in patients with advanced Merkel cell carcinoma and an evaluation of genomic correlates of response

BACKGROUND: The use of targeted therapy remains a treatment consideration for some patients with advanced Merkel cell carcinoma (MCC). However, supportive data on the use of targeted therapy approaches are limited. Thus, we sought to evaluate the responsiveness of targeted agents in patients with advanced MCC. METHODS: An institutional MCC database identified patients who were treated with targeted therapy. For the purpose of this study, targeted therapy was defined as any multi‐targeted tyrosine kinase inhibitor or inhibitor of the PI3K‐pathway. Clinical benefit was defined as complete response, partial response, or stable disease (SD) ≥6 months. A subset of patient samples underwent next‐generation sequencing (NGS), Merkel cell polyomavirus testing, and PD‐L1/PD‐1 expression testing. RESULTS: Nineteen patients with MCC treated with targeted therapy were identified, 21 targeted therapy regimens were evaluable for response in 18 patients. Four of twenty‐one (19%) of evaluable regimens were associated with clinical benefit with the best overall response of SD. The durations of SD were 13.6 months (59 weeks), 9.7 months (42 weeks), 7.6 months (33 weeks), and 7.2 months (31 weeks). Of the four patients who derived clinical benefit, three were treated with pazopanib alone and one was treated with pazopanib plus everolimus. No difference in the rate of clinical benefit between molecular disease subtypes was detected nor was associated with any specific genomic alteration. CONCLUSION: In our series, targeted agents elicited a disease control rate of 19% in patients with advanced MCC, with a best overall response of SD. Pazopanib alone or in combination exhibited a rate of disease control of 36% (4 of 11 with SD ≥6 months).