Molecular mechanisms and therapeutic targets in genital tract malignant melanomas

Abstract

Female genital tract malignant melanomas are rare and aggressive neoplasms. At presentation, most women already have advance disease and complete surgical resection is often difficult to achieve and adjuvant therapy has not been found useful. Targeted drugs against tumors which bear mutations involving C-KIT and BRAF genes are available but their effectiveness is unknown. The uncertainty may be related to complex molecular mechanisms which are poorly understood and the fact that almost all female genital tract melanoma patients died from tumor and long-term success of using these drugs could not be determined. Immune checkpoint inhibitors have emerged to be beneficial in the treatment of advance cutaneous melanomas but its potential in genital tract melanoma has yet to be evaluated. PD-L1 immunohistochemistry and other potential biomarkers also have not been widely investigated. We studied a rare collection of clinical cases of female genital tract melanomas and genital melanoma cell lines. We assessed potential immunotherapy biomarkers, evaluated the status of several commonly dysregulated genes in the mitogen-activated protein kinase (MAPK) pathway and correlated their mutational and/or expressional statuses. The in-vitro effects of C-KIT and BRAF inhibitors on genital melanoma cell lines were also appraised. There were 55 genital tract melanomas, 20 were vulvar and 35 were non-vulvar (vaginal and cervical. After a median follow-up of 14 months, only seven vulvar melanoma patients (65%) were alive, the rest died. Ninety-four per cent of patients who had non-vulvar melanomas died. Favorable prognostic factors identified were a vulvar location, absence of lymph node metastasis at presentation, and high CD8+ and CD4+ tumor infiltrating lymphocyte counts. Adverse prognostic factors included a large size (33 mm) and a mitotic count of 10 per 10 high power fields. PD-L1 expression was found in 57.9% and 48.5% of vulvar and non-vulvar melanomas, respectively. Loss of mismatch repair proteins expression was found in 21.1% of vulvar and 8.6% of non-vulvar melanomas. BRAF V600E (VE1) and PAK1 immunohistochemical expressions in all clinical cases were 14.5% and 28%, respectively. Mutations involved C-KIT and BRAF were found in a minority of the clinical samples but no NRAS mutation was detected. There was no correlation between C-KIT mutational status and protein expression. Four previously unreported pathogenic C-KIT mutations, two novel C-KIT mutations, and two unreported pathogenic BRAF mutations were discovered. Imatinib was effective in the inhibition of melanoma cell lines but sunitinib was not. Sorafenib was highly toxic in-vitro, and mirrored the clinical toxicity reported. Patients with female tract genital melanomas have dismal prognosis and every effort should be made to identify actionable mutational targets and assessment of relevant biomarkers should be done. The clinical decision for using targeted therapies must made with caution because C-KIT and BRAF inhibitors are highly toxic. If resources are available, mutational analysis should not be limited to screening for hotspot mutations as other potentially actionable gene mutations may be missed. The decision of utilizing immune-checkpoint blockade therapy should be made after evaluation of biomarkers. (Word count: 486)