Patterns of histologic response to neoadjuvant targeted therapy in patients with BRAF mutant melanoma.

Abstract

9584 Background: While BRAF and MEK inhibitors are approved for patients with BRAF V600 + unresectable/metastatic melanoma, their role in the neoadjuvant setting is less well defined. Results from small trials have noted robust response rates, but less is known about histological patterns of response in resected tumor specimens and relation to outcome in these patients (pts). Methods: In a retrospective study, we analyzed the clinical and pathologic patterns of response to neoadjuvant BRAF ± MEK inhibitor therapy in pts with locally advanced melanoma subsequently rendered disease free with surgery. Results: Twenty pts were identified, nine with stage IIIC and 11 with stage IV melanoma. Seven patients received neoadjuvant vemurafenib (VEM), 12 received dabrafenib + trametinib (D+T), and one encorafenib + binimetinib. The median duration of treatment was 7.8 months. Seven patients (35%) had a pathologic complete response (pCR); six of them had received combination therapy, 5 with D+T, 1 VEM with an HSP90 inhibitor. Four distinct histologic patterns were observed in the resected tumor specimens: necrotic, fibrotic/melanotic (tumoral melanosis), hyalinized, or mixed. With median follow-up of 25 months (range 1-60), six pts (30%) had experienced recurrence; three developed CNS metastases. Four of the six patients had received neoadjuvant D+T; three were restarted on their prior targeted therapy at recurrence and all responded. All 6 pts with recurrence had residual disease in the surgical specimen; three had no necrosis identified. In contrast to the 13 pts with persistent tumor, none of the 7 pCR pts has relapsed (p = 0.05). There was a trend towards improved relapse-free-survival (RFS) with a pCR, with a 1 yr of RFS-rate of 50.4% vs 100% in pCR.(p = 0.08) Of the 14 patients without subsequent recurrence, 9 had either a pure necrotic histology, or a mixed histological pattern that included necrosis. Conclusions: In locally advanced or M1a BRAF mutant melanoma, attaining a pCR to neoadjuvant targeted therapy may correlate with improved patient outcomes and be more likely achieved with combination therapy. Presence of necrosis in the surgical specimen appears be a favorable prognostic factor.