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    • Of KIT mutations seven occurred in

    2018-11-01

    Of 15 KIT mutations, seven occurred in EPI-001 11, five in exon 13, three in exon 17, and none in exon 18 (Table 2). The most common mutation was L576P (n = 6) and K642E (n = 6), followed by D820Y (n = 2), and finally Y559D (n = 1), L657F (n = 1), and G827R (n = 1). Although only three of 20 (15%) recurrent/metastatic melanomas had a KIT mutation, the majority of them were D820Y (2/3). By contrast, D820Y was not detected in all primary melanomas at diagnosis, which had a KIT mutation rate of 20% (12/61) and approximately 92% (11/12) occurred in exons 11 and 13. There were three cases of in situ melanoma in this study. Two of them had DNA sequence data, and were wild type for the analyzed KIT exons.
    Discussion By collecting unselected cases from two hospitals that are not known for being dermatology referral centers, we analyzed 85 melanomas in this study. A larger series of melanoma in Taiwan was studied by Chang et al in 2004, who collected 181 cases from a single institute that is known for being a referral center for dermatology patients. Both our series and theirs showed a similar median age (62 vs. 61 years), a similar male-to-female ratio (1:1.23 vs. 1:1.13), and a similar percentage of metastatic disease at the time of diagnosis (24% vs. 25%), suggesting that both were representative for melanoma patients in Taiwan. It is of interest that both cohorts pointed out that acral melanoma is a common type of melanoma in Taiwan (Chinese population) and mucosal melanoma is not uncommon either. By contrast, acral melanoma is uncommon in Caucasians, accounting for less than 10% of all melanomas, and mucosal melanoma is even rare, accounting for only 1.2% of all melanomas in Western countries. To our knowledge, KIT mutation rates in cutaneous, mucosal, and acral melanomas have so far been compared in four studies (Table 3). Two of them showed that the KIT mutation rate was lower in cutaneous melanomas than in acral and mucosal melanomas in American patients. However, one of the four studies, which analyzed Chinese patients, showed no significant difference of KIT mutation rates among these three types of melanoma. These opposite results may suggest a racial difference in KIT mutation frequency among cutaneous, mucosal, and acral melanomas. However, our study on Chinese patients showed that the KIT mutation rate in mucosal and acral melanomas was threefold higher than that in cutaneous melanoma, suggesting that there is no racial difference in this issue. When putting all analyzed patients in these five studies together (Table 3), we noticed that the KIT mutation rate in cutaneous melanomas (9%) is indeed lower than that of acral (16%) and mucosal (15%) melanomas. For acral melanoma, EPI-001 the KIT mutation rate (25%) in our series is close to that of Beadling et al (23%) and Carvajal et al (21%), but is higher than that of Curtin et al (11%) and Handolias et al (6%). We have no explanation for this disparity. However, it should be addressed that acral melanoma is usually very small in size, thus making a false negative result difficult to avoid. To date, KIT mutations have been analyzed in 457 acral melanomas (Table 4). The average KIT mutation rate in these patients is approximately 14%. As for mucosal melanoma, the KIT mutation rate in our series was 22%, similar to the findings of Curtin et al, who showed a mutation rate of 21%. Since 2006, there have been 15 reports including ours that analyzed KIT mutations in mucosal melanomas (Table 5). From these 672 cases, we noticed that the KIT mutation rate in mucosal melanoma is approximately 15%, ranging from 5% (Korea) to 38% (Australia). In this study, we found that KIT mutations occur most commonly in the anorectum and genitourinary tract. Although our series is small in sample size, this trend is compatible with the data when we accumulated all analyzed patients from these 15 reports together (Table 5). Of interest, none of our mucosal melanomas of the head and neck had KIT mutation and eight of 11 melanomas of this category occurred in the nasal cavity/sinus.