P28 Pathologic characteristics of BRAF V600E mutation in negative cutaneous melanoma

Melanoma is one of the aggressive cancer types. Mutations that lock the BRAF protein in an active state may cause excessive signaling in the pathway, leading to uncontrolled cell growth and survival. Primarily among the BRAF mutations observed in melanoma, over 90% are supposed to be at codon 600, resulting in substitution of glutamic acid for valine, V600E (T>A transversion) located in exon 15, BRAFV600E. Of particular interest is BRAF negative melanoma. This type of melanoma is not sensitive to BRAF inhibitors and approaches to therapy require further study. We aimed to investigate the frequency of BRAF V600 mutations in 80 patients with primary melanoma and determine the relationship between mutations and clinical/pathologic features. Genomic DNA was extracted from biopsy specimens with prevalent percentage of tumor cells by DNA-sorb B isolation kit (Amplisense, Russia). BRAF V600E mutation was estimated by real-time PCR-based assay for the BRAF V600E mutation allele-specific DNA test (BioLink, Russia). Breslow thickness was assessed by applying commercial Infinity Capture, Infinity Analyze Software. The lymphocytic infiltration was determined in all tumors and classified as “brisk”, “nonbrisk”, and “absent” according to criteria established by Clark et al. Tumor infiltrating lymphocytes (TIL) were identified as lymphocytes within tumor nodes. “Brisk” infiltrate was determined in case of a diffuse presence of lymphocytes within tumor, “non-brisk” infiltrate was in focal location of lymphocytes and “absent” if no lymphocytes were present in a tumor. Mitotic activity was determined as mitotic count on 10 high power fields. For all patients, clinical and pathologic features were tested for significant association with BRAF V600E mutation status using simple cross tabulations, Fisher’s exact test, Pearson’s χ2 test, and/or non-parametric Mann–Whitney U test. The P values lower 0.05 were considered as significant. BRAF V600E mutation was detected in 41.25% of tested tumours. Patients with BRAF-mutant and non-BRAF mutant melanoma were matched by age and gender. Superficial spreading melanomawas observed in 66.2% of patients with wild-type BRAF, nodular melanoma in 21.2%, both lentigo-melanoma and acral-lentiginous melanomain 6.3% and mucosal melanoma in 1 3.0% of patients. In wild-type BRAF melanoma patients, 59.7% tumors had “brisk” infiltrate, 14.8% – “non-brisk”, and 12 25.5% had no infiltrate. There was no found correlation between BRAF status and tumor localization, clinico-pathological type of tumor, TIL status, Breslow thickness and mitotic rate. However, when cases were stratified by age, it was revealed that melanoma patients aged above 80years were preferentially BRAF-negative (p