FDG-PET/CT response and prediction of pathological response to neoadjuvant nivolumab and ipilimumab for clinical stage III melanoma.

Abstract

9585 Background: Neoadjuvant immunotherapy with nivolumab 3mg/kg and ipilimumab 1 mg/kg (N3+I1) for two cycles for clinical stage III melanoma have shown rates of major pathological response (MPR) of approximately 60%.The prognosis of this group seems to be excellent so far. On the other hand, patients classified as pathological non-responders have a worse outcome and early identification of this group may allow us to tailor the treatment before surgery. Methods: We conducted a multicenter retrospective analysis of patients with clinical stage III melanoma treated with neoadjuvant N3+I1 for two cycles who did baseline and pre-operative 18F-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 2023, 28 patients with clinical stage III melanoma treated with N3+I1 who had baseline and preoperative 18F-FDG PET were identified. Gender: 20 (71%) males, median age (range):55 (34-78), BRAFV600E/K mut: 15(53%), positive nodes on baseline PET/CT:1 = 26 (92%), 2 = 1(4%), and 3 = 1(4%). All known lesions identified by CT scan were also captured by FGD-PET/CT. Site of node(s): axilla = 12 (43%), cervical = 10 (36%), and inguinal = 6(21%). All but one patient received 2 cycles of N3+IP1(1 patient had grade 3 toxicity and received only one cycle). Pathological response: MPR = 19(68%), non-MPR: 8 (28%), and 1(4%) did not undergo surgery due to widespread progression. An increase in maximum SUV and/or appearance of new lesion(s), n = 8(28%), was correlated to non-MPR or metastatic disease in all cases, including a patient who developed sarcoidosis-like reaction with increase of SUV in the index lesion (+68%) and appearance of inflammatory mediastinal lymph-nodes. The median increase was (range): +73% (+11% to 483%). Reduction or stable maximum SUV with no appearance of new lesion, n = 20 (72%), was associated with MPR in 19 patients (95%). One patient,who had G3 colitis (with the need of infliximab), had 32% of reduction in maximum SUV but 100% of viable tumor cells on pathological report. The median decrease (range) was -76% (-1.2% to -100%). Conclusions: FGD-PET/CT may help to predict pathological response in patients with clinical stage III melanoma who undergo to neoadjuvant nivolumab and ipilimumab.