1149P - Prognosis for patients with metastatic Merkel cell carcinoma with a complete response on avelumab treatment

Background

Immune checkpoint inhibitor (ICI) treatment of patients with metastatic Merkel cell carcinoma (mMCC) has shown high response rates, ranging from 33%-73%. The ideal duration of treatment is however currently unknown. We aimed to evaluate if avelumab treatment for mMCC can be safely stopped after 1 year of treatment and confirmed complete response (CR) by FDG-PET/CT.

Methods

Patients who received >one dose of avelumab treatment for mMCC between November 2017 and February 2022 were included in this study. Treatment was discontinued in case of a FDG-PET/CT confirmed CR after 1 year (26 cycles) of avelumab, or a CR and unacceptable toxicity earlier on. Primary endpoint was recurrence free survival (RFS).

Results

Sixty-five patients were included: 25 (38%) had a FDG-PET/CT confirmed CR at discontinuation of avelumab. In those 25 patients, reasons for discontinuation of treatment were completion of 1 year of treatment in 13 patients (52%), toxicity in 5 patients (20%) and patient preference in 7 patients (28%). Median duration of treatment in this group was 11 months (IQR 6.1-11.7). Median follow-up was 27 months (IQR 15.8-33.8). The 12 months RFS was 88% (95% CI 0.74-1) and median RFS was not reached. Two patients (9,5%) had a recurrence, at 4 and 7 months after discontinuation of treatment.

Conclusions

Avelumab treatment for patients with mMCC can be safely discontinued after one year of treatment and a PET/CT confirmed CR, as responses appear to be durable, with a 12 months RFS of 88%.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

A.C.J. van Akkooi: Financial Interests, Institutional, Advisory Board: Amgen, Bristol Myers Squibb, Novartis, MSD - Merck, Merck-Pfizer, Pierre Fabre, Sanofi, Sirius Medical, 4SC, Provectus; Financial Interests, Institutional, Research Grant, NIVEC study: Amgen; Financial Interests, Institutional, Research Grant: Merck-Pfizer. All other authors have declared no conflicts of interest.