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Melanoma: Double BRAF mutation, double chance to treat?

Dear Editor, Metastatic melanoma is one of the deadliest cancers and carries a poor prognosis. Around 50% of melanomas harbor a BRAF activating mutation. Over 97% of these mutations are situated in codon 600, with the most common (80-90%) being the substitution of valine to glutamic acid (V600E), followed by valine to lysine (V600K; 5%-12%) or aspartic acid (V600D; <5%) or arginine (V600R; <5%). Normally V600E mutation occurs when thymine is substituted with adenine at nucleotide 1799 (1799T>A). Occasionally, this mutation can be associated with another substitution (adenine replaces guanine) taking place at nucleotide 1800 (“complex” mutation 1799_1800 TG>AA) only detected by Next Generation Sequencing method. These mutations enhance BRAF activity, leading to an increase in phosphorylation of MAPK/ERK pathway downstream molecules, especially MEK, resulting in uncontrolled cell proliferation. Dabrafenib plus trametinib is a combination targeted therapy that inhibits BRAF and MEK, and it is an approved treatment for metastatic melanomas harboring BRAF V600 mutations. Nevertheless, drug registration studies included only BRAF V600 E/K mutations and clinical experience in patients harboring BRAF rare mutations is based on anecdotal case reports. Herein, we report a case of metastatic melanoma with co-occurring BRAF V600E and V600D mutation successfully treated with dabrafenib and trametinib. A 45-year-old woman presented to our outpatient clinic with a recent history of left axillary lymphadenopathy. Therefore, we performed regional lymphadenectomy. One of 10 exanimated lymph nodes was positive for melanoma metastasis. BRAF mutation analysis was positive for V600E and V600D. A staging full-body CT revealed left pectoral lymphadenopathy and, thus, the patient underwent a second lymphadenectomy. Histological examination of the removed lymph nodes revealed another melanoma metastasis showing atypical cells with immunoreactivity for S-100 and MITF. After a full-body skin exam, we were not able to detect any lesion consistent with a cutaneous melanoma other than an achromic lesion on the upper back, that we decided to excise. Histological examination reported a completely regressed melanocytic lesion. She also received rectal and genital examination, ENT and ophthalmological visit with no evidence of other suspicious lesions. Consequently, the patient started dabrafenib and trametinib therapy with complete and stable disease regression after 18 months of treatment, confirmed by full-body CT (Figure 1A,B). V600D is an infrequent BRAF mutation present in 0.08% of all melanoma patients. The coexistence of V600D and V600E mutation is even rarer. BRAF analysis was performed using qPCR Easy Braf KIT (Diatech). This kit allows the detection of low percentages of mutated allele, in presence of high amounts of wild-type genomic DNA, by real-time amplification with sequence-specific probes marked with FAM and HEX (LOD down to 0.5%), in 2 hours execution time. The importance of our case lies in the fact that there is a lack of studies involving the treatment of melanomas harboring V600 rare mutations and double mutations. Interesting in vitro and in vivo studies indicate that V600DBRAF/V600EBRAF mutation represent an