Incidence of cutaneous melanoma has increased during last decades in Western population [1, 2]. Several risk factors have been reported. A light phototype (especially when associated with excessive sun exposure and/or increased incidence of sunburns), a large number of acquired common nevi, and the occurrence of atypical nevi have been associated with a higher risk of melanoma [3, 4]. Among others, family history of melanoma (presence of two or, mainly, three or more affected relatives) confers the highest risk for the development of the disease [3, 5]. Nevertheless, patients with cutaneous melanoma present a higher incidence of second or even additional melanomas (risk seems to be highest in the first years after diagnosis of the first melanoma and decreases progressively with time) [6, 7]. However, subsequent primary melanomas have been found to be significantly thinner than index lesions , possibly due to increased surveillance and not to differences in tumor biology [9–11]. In patients with multiple primary melanoma (MPM), the disease staging is based on the melanoma with the worst prognostic features .
From the pathogenetic point of view, the mitogen-activated protein kinase (MAPK) signal transduction pathway (including the cascade of NRAS, BRAF, MEK1/2, and ERK1/2 proteins) has been reported to play a major role in both the development and progression of melanoma [13, 14]. The increased activity of ERK1/2 proteins, which is constitutively activated in melanomas mostly as a consequence of mutations in upstream components of the pathway, has been implicated in rapid melanoma cell growth, enhanced cell survival and resistance to apoptosis [15, 16]. Oncogenic mutations of BRAF, all constituted by single amino acid substitutions, have been found in approximately 8% of all types of human cancer, including colorectal, ovarian, thyroid, and lung cancers as well as in cholangiocarcinoma and hepatocellular carcinoma [15, 17, 18], but their highest rates remain those observed in melanoma. Overall, slightly less than half of melanomas carry activating mutations in the BRAF gene [19, 20], regardless of the mutation screening approach used . The affirmation of new drugs inhibiting some mediators of the MAPK pathway, including mutated BRAF and activated MEK, has led to major advances in the treatment of patients with melanoma .
A less common primary pathway which stimulates cell proliferation, without MAPK activation, seems to be the reduction of RB (retinoblastoma protein family) activity by CyclinD1 or CDK4 amplification or RB mutation (impaired RB activity through increased CDK4/cyclin D1 could substitute for the MAPK activation and initiate clonal expansion) . Nevertheless, impairment of the p16CDKN2A protein, which acts as an inhibitor of melanocytic proliferation by binding the CDK4/6 kinases and blocking phosphorylation of the RB protein, may also lead to uncontrolled cell growth as well as to increased aggressiveness of transformed melanocytic cells [23, 24].
It has been reported that melanomas on skin not chronically exposed to sun usually carry a mutated BRAF whereas those arising from chronically sun-damaged (CSD) skin infrequently have BRAF mutations but present an increased copy number of the proliferation-controlling CyclinD1 (CCND1) or cKIT genes, with subsequent increased expression of the correspondent proteins [25–28]. Overexpression of the CyclinD1 gene is commonly observed in several human cancers, including breast, head and neck, and bladder cancers . In melanoma, the elevated intracellular concentration of CyclinD1, related to the amplification of the gene locus at chromosomal level, has been implicated into the resistance to both BRAF and MEK inhibitors since it promotes a MAPK-independent cell proliferation [27, 30]. With no stratification for anatomical location, amplification of cKIT has been reported in about 7% of all cutaneous melanomas [25, 31]; its frequency increase up to 30% or more in acral and CSD melanomas as well as in melanomas carrying a cKIT mutation (prevalence is even higher in Chinese population ) [25, 31, 33].
In this study, we aimed at assessing the frequency and distribution of alterations in candidate genes (BRAF, cKIT, CyclinD1) involved in pathogenesis of melanoma in a large series of patients with synchronous or asynchronous MPM lesions.