34 | Dissecting the spectrum of rare BRAF mutations in melanoma: a nation-wide study by the Italian Melanoma Intergroup

Francesco Spagnolo^1|2, Bruna Dalmasso³, Maria Chiara Scaini⁴, Laura Cendron⁵, Monica Rodolfo⁶, Ilaria Mattavelli⁷, Elena Tamborini⁸, Francesca Collina⁹, Gerardo Ferrara, Gabriele Madonna¹⁰, Carlo Cota¹¹, Elisa Melucci¹², Stefania Tommasi¹³, Martina Ubaldi¹⁴, Roberta Depenni¹⁵, Andrea Carugno¹⁶, Riccardo Marconcini¹⁷, Laura Orgiano¹⁸, Maurizio Lombardo¹⁹, Simona Sola²⁰, Cristina Pellegrini²¹, Francesca Castiglione²², Matteo Gasparotto^5|23, Alireza Jorkesh⁵, Stefania Pellegrini⁴, Edoardo Raposio¹, Andrea Boutros², Enrica Teresa Tanda², Michele Guida²⁵, Pietro Quaglino²⁶, Giuseppe Palmieri²⁷, Daniela Massi²², Paolo Antonio Ascierto¹⁰, Mario Mandalà*²⁸, Chiara Menin*⁴, Paola Ghiorzo*²⁴, Lorenza Pastorino*²⁴, for the Italian Melanoma Intergroup²⁹ | ¹Department of Surgical Sciences and Integrated Diagnostics, DISC, Plastic Surgery Division, University of Genoa; ²IRCCS Ospedale Policlinico San Martino, Genova; ³IRCCS Ospedale Policlinico San Martino, Cancer Genetics, Genoa; ⁴Immunology and Molecular Oncology Unit, Veneto Institute of Oncology - IOV IRCCS, Padua; ⁵Department of Biology, University of Padua, Padua; ⁶Unit of Translational Immunology, Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan; ⁷Melanoma Surgical Unit, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan; ⁸Department of Diagnostic Innovation, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan; ⁹Pathology Unit, Istituto Nazionale Tumori, IRCCS - Fondazione G. Pascale, Napoli; ¹⁰Melanoma, Cancer Immunotherapy and Innovative Therapies Unit, Istituto Nazionale Tumori IRCCS Fondazione G. Pascale, Napoli; ¹¹Dermatopathology Unit, San Gallicano Dermatological Institute IRCCS, Rome; ¹²Pathology Unit, IRCCS Regina Elena, National Cancer Institute, Rome; ¹³Molecular Diagnostics and Pharmacogenetics Unit, IRCCS Istituto Tumori "Giovanni Paolo II", Bari; ¹⁴Unit of Medical Oncology, University of Perugia; ¹⁵Department of Oncology and Hematology, University of Modena and Reggio Emilia, Modena; ¹⁶Department of Medicine and Surgery, University of Insubria, Varese; ¹⁷Medical Oncology Unit, Azienda Ospedaliero-Universitaria Pisana, Pisa; ¹⁸Department of Medical Oncology, University of Cagliari, Cagliari; ¹⁹Division of Dermatology, Department of Medicine and Surgery, Ospedale di Circolo e Fondazione Macchi, ASST dei Sette Laghi, Varese; ²⁰Surgical Pathology, Galliera Hospital, Genoa; ²¹Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila; ²²Histopathology and Molecular Diagnostics, Careggi University Hospital, Florence, Italy and Section of Pathology, Department of Health Sciences, University of Florence, Italy; ²³Department of Translational Brain Research, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany. ²⁴Department of Internal Medicine and Medical Specialties, University of Genoa; ²⁵Rare Tumors and Melanoma Unit, IRCCS Istituto Tumori Giovanni Paolo II, Bari; ²⁶Dermatology Clinic, Department of Medical Sciences, University of Turin; ²⁷Immuno-Oncology & Targeted Cancer Biotherapies, University of Sassari - Unit of Cancer Genetics, IRGB-CNR, Sassari; ²⁸University of Perugia, Medical Oncology Unit, Santa Maria Misericordia Hospital, Perugia; ²⁹Italian Melanoma Intergroup, IMI, Italy. *These authors equally contributed to this work.

Introduction: Non-V600E/K BRAF mutations have been reported in melanoma, but data on their clinical relevance are conflicting. This study investigated the distribution, prognostic role and functional impact of rare BRAF mutations in melanoma.

Methods: We retrospectively assessed frequency, response to therapy and outcome of rare BRAF mutations compared to V600E/K in cases from 19 Italian Melanoma group (IMI) centers.

Results: 258/14081 samples (1.8%) harbored rare BRAF mutations, 40% encompassing codon 600. Overall and progression-free survival (OS, PFS) following targeted therapy with BRAF/MEK inhibitors were comparable to V600E/K mutant melanoma (HR=0.85 and 0.89, p>0.1) (Figure 1). Response to targeted therapy was lower, albeit not significantly, in rare BRAF mutant melanomas compared to V600E/K (48 vs 66%, p>0.05). OS, PFS, and objective response in cases treated with immunotherapy were unaffected by BRAF status. Molecular dynamics simulation assessing whether selected BRAF variants affected BRAF structure similarly to V600E, showed variable degrees of destabilization towards constitutive protein activation, particularly for mutations encompassing codons 599-601.

Conclusions: Rare BRAF mutations can modify BRAF kinase activity, including a subset of mutations outside, but close to codon 600. Molecular approaches able to detect rare BRAF mutations could identify additional melanoma cases eligible for therapies with BRAF/MEK inhibitors.

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Figure 1.