FDG-PET/CT response and outcome of neoadjuvant immunotherapy for clinical stage III melanoma.

Abstract

e21569 Background: Neoadjuvant immunotherapy with nivolumab 3mg/kg and ipilimumab 1mg/kg for two cycles(N3+I1) or anti-PD1 for 3-8 weeks for clinical stage III melanoma have shown rates of pCR/near-pCR about 60% or 30%, respectively. The prognosis of this group seems to be excellent so far. On the other hand, patients classified as pathological non-response have a worse outcome and early identification of this group may allow us to tailor treatment before surgery. Methods: We conducted a retrospective analysis of patients with clinical stage III melanoma treated with neoadjuvant immune checkpoint blockade who did baseline and pre-operative FDG-PET/CT. The total number of FGD avid lesions and the percentual difference between the maximum SUV per lesion was calculated. The pathological results were correlated to FGD-PET/CT findings. Results: Between January 2019 and January 2021, nine patients with clinical stage III melanoma were identified. Six patients received Nivolumab 3m/kg and Ipilimumab 1mg/kg for two cycles and 3 received anti-PD1 for 60 days. Baseline FDG-PET/CT showed just one avid lesion in 7 patients, 2 avid lesions in one patient and 3 avid lesions in one patient. All known lesions identified by CT scan were also captured by FGD-PET/CT. After the neoadjuvant treatment, 4 patients achieved pCR/near-pCR. All of them were treated with N3+I1. Two of them had metabolic complete response (including the one with 3 PET- avid lesions) and 2 had reduction on FDG concentration (-31% and – 76%). Three patients had absence of response: 100% of viable tumor cells (VTC), all of them with increase in FDG concentration (+12% to + 307%) and appearance of a new lesion in one case. Two out of them were treated with anti-PD1. One patient had partial response (40% of VTC). Interestingly, this patient developed sarcoidosis-like reaction with increase of SUV in the index lesion (+68%) and appearance of mediastinal lymph-nodes. One patient, who had two lesions, presented a mixed response: complete response in one and 90% of VTC in the other. FDG-PET/CT was able to detect both responses (metabolic complete response and increase of FGD concentration of 17%, respectively). Conclusions: Reduction in FGD-PET/CT concentration with no appearance of new lesion(s) is associated with significant pathological response. An increase of SUV or appearance of new lesion(s) should be carefully interpreted.