Approximately 50% of melanomas contain BRAF mutations, which occur in a greater proportion of melanomas found on sites of intermittent sun exposure.1BRAF-mutated melanomas have been associated with high levels of early-life ambient UV exposure, especially between ages 0 and 20 years.2 In addition, studies have shown that BRAF-mutated melanomas commonly are found on the trunk and extremities.1-3BRAF mutations also have been associated with younger age, superficial spreading subtype and low tumor thickness, absence of dermal melanocyte mitosis, low Ki-67 score, low phospho-histone H3 score, pigmented melanoma, advanced melanoma stage, and conjunctival melanoma.4-7BRAF mutations are found more frequently in metastatic melanoma lesions than primary melanomas, suggesting that BRAF mutations may be acquired during metastasis.8 Studies have shown different conclusions on the effect of BRAF mutation on melanoma-related death.5,9,10
The aim of this study was to identify trends in BRAF V600E–mutated melanoma according to age, sex, and melanoma-specific survival among Olmsted County, Minnesota, residents with a first diagnosis of melanoma at 18 to 60 years of age.
Methods
In total, 638 patients aged 18 to 60 years who resided in Olmsted County and had a first lifetime diagnosis of cutaneous melanoma between 1970 and 2009 were retrospectively identified as a part of the Rochester Epidemiology Project (REP). The REP is a health records linkage system that encompasses almost all sources of medical care available to the local population of Olmsted County.11 This study was approved by the Mayo Clinic Institutional Review Board (Rochester, Minnesota).
Of the 638 individuals identified in the REP, 536 had been seen at Mayo Clinic and thus potentially had tissue blocks available for the study of BRAF mutation expression. Of these 536 patients, 156 did not have sufficient residual tissue available. As a result, 380 (60%) of the original 638 patients had available blocks with sufficient tissue for immunohistochemical analysis of BRAF expression. Only primary cutaneous melanomas were included in the present study.
All specimens were reviewed by a board-certified dermatopathologist (J.S.L.) for appropriateness of inclusion, which involved confirmation of the diagnosis of melanoma, histologic type of melanoma, and presence of sufficient residual tissue for immunohistochemical stains.
All specimens were originally diagnosed as malignant melanoma at the time of clinical care by at least 2 board-certified dermatopathologists. For the purposes of this study, all specimens were rereviewed for diagnostic accuracy. We required that specimens exhibit severe cytologic and architectural atypia as well as other features favoring melanoma, such as consumption of rete pegs, pagetosis, confluence of junctional melanocytes, evidence of regression, lack of maturation of melanocytes with descent into the dermis, or mitotic figures among the dermal melanocyte population.
The available tissue blocks were retrieved, sectioned, confirmed as melanoma, and stained with a mouse antihuman BRAF V600E monoclonal antibody (clone VE1; Spring Bioscience) to determine the presence of a BRAF V600E mutation. BRAF staining was evaluated in conjunction with a review of the associated slides stained with hematoxylin and eosin. Cytoplasmic staining of melanocytes for BRAF was graded as negative, focal or partial positive (<50% of tumor), or diffuse positive (>50% of tumor)(Figure 1). When a melanoma arose in association with a nevus, we considered only the melanoma component for BRAF staining. We categorized the histologic type as superficial spreading, nodular, or lentigo maligna, and the location as head and neck, trunk, or extremities.
FIGURE 1. Examples of staining of melanocytes in melanomas for BRAF V600E. A, Negative cytoplasmic staining of melanoma melanocytes. Positive and negative controls that were run simultaneously with each specimen showed appropriate reactivity. All examples had immunohistochemical staining (anti–BRAF V600E, clone VEI; original magnification ×10). B, Focal or partial positive (<50% of tumor cells) cytoplasmic staining of melanoma melanocytes. C, Diffuse positive (>50% of tumor cells) cytoplasmic staining of melanoma melanocytes.