In this study, the BRAF V600 mutation was found in 53.85% of the nodular melanoma cases. This result resembles the mutation prevalence found in Caucasian populations, which range around 40-60% (10). Data on the nodular subtype from Asia is scarce with two studies reporting rates of 50% and 29.4% from Japan and Turkey, respectively (11,12). The outcomes of our research are especially at odds with the result of our previous study using RT-PCR, which report a 10% BRAF V600 prevalence among Indonesian nodular melanomas (8). The higher prevalence found in this study may arise from the difference in methods. In terms of sensitivity, pyrosequencing is superior compared to high-resolution melt PCR studies (13). In a comparation of methods, RT-PCR detected 98% of cases while pyrosequencing had 100% sensitivity (14).
Analysis of the VAF in our study shows a wide variation of 5.07% to 94.70%, with an average of 29.05%. However, most of the cases had low VAFs, with 13 (61.9%) specimens below 20% and 4 (19.05%) below 10%. For comparison, a previous study on BRAF mutation profiling in melanomas report a VAF below 20% only in 28% of samples and below 10% in 13% (15). Given the dominance of low VAF percentages, many mutation-positive tumors which would have been detectable by pyrosequencing would likely go undetected in RT-PCR studies. The low VAF distribution in the Indonesian population in general may explain the difference in the mutation prevalence found when using RT-PCR and pyrosequencing despite the slight differences in sensitivity. The difference might be also influenced by the low sample size.
When compared to other Asian countries, the BRAF V600 prevalence in this study is relatively high. This mutation is found in 11.9% to 41.8% of Asian melanoma cases in general (5,12,16,17). The only two studies on Asian nodular melanoma cases reported the mutation prevalence at 29.4% and 50% (11,12). This suggests that Indonesian melanoma cases have a high BRAF V600 mutation prevalence, but at low intratumoral mutation rates. Variations in melanoma subtype, ethnicity, and different mutation detection methods may partially be responsible for the differences found.
No significant associations were found with clinicopathologic characteristics. The general trends, such as younger age, central location, absent of ulceration, and presence of lymphovascular invasion, mirror the findings of previous Asian studies. In our previous study done with RT-PCR in nodular melanoma patients in Indonesia (8), central location and lymphovascular invasion were correlated with BRAF V600 mutation. The differences could have been caused by the low VAFs found in this study, which may cause mutation-positive tumor to behave like mutation-negative tumors instead. Another factor that possibly dissipated any correlations would be the unbalanced proportions of patient characteristics, as the subjects in this study were dominated by advanced extremity-located melanomas.
The presence of TILs is one of the indicators of the immune response to melanomas and is associated with better prognosis. Oncogenic BRAF mutations are associated with immune escape of tumor cells and a lower presence of TILs (18). In our study, BRAF mutation-positive tumors tended to have a lower presence of TILs, despite not reaching statistical significance. Along with the other associations, this trend suggests that Indonesian nodular melanoma cases with the BRAF V600 mutation tend to have worse prognoses than cases with the wild-type BRAF.
BRAF mutation testing and targeted therapy has yet to be used in melanoma case management in Indonesia. These are due to limitations in both availability and costs. Currently, BRAF mutation testing and BRAF inhibitors are not included in the Indonesian national health insurance program. Healthcare centers that provide molecular mutation testing are also still scarce. Most melanoma patients in Indonesia cannot afford the price of completing a whole cycle of BRAF inhibitor therapy. As a result, BRAF V600 mutation testing is only done in research settings and treatment for melanomas is commonly limited to surgery and cytotoxic chemotherapy (dacarbazine).
These difficulties suggest that currently it is only possible to provide molecular testing and treatment to a select portion of patients who would most likely benefit from it. The mutation rate could be a potential marker to predict response to targeted therapy. A study shows that higher BRAF V600 mutation VAFs are associated with better response rates to vemurafenib (19). Quantification of BRAF mutation levels may help select patients with the best potential for molecular treatment.
Another option would be to use a less sensitive method for clinical usage in Indonesia, such as RT-PCR. The facilities for this method are more widely available, easier, and cheaper in Indonesia than pyrosequencing. Although only tumors with higher VAFs would be detected by PCR studies, this would mean that the identified tumors will have better treatment response. Thus, using PCR methods for mutation detection may be more feasible and cost-effective for prognostic and therapy decision-making in Indonesia.
Our previous research provided the BRAF V600 mutation prevalence in Indonesian skin nodular melanoma cases. This research improved it using a more sensitive method and specified the mutation subtype. Through these studies, we have advanced knowledge on BRAF V600 mutation profiles in primary skin nodular melanoma cases in Indonesia. This information will help develop prognostication and treatment decision-making for Javanese patients.