Aya Uchiyama

Polyclonality of BRAF mutations in primary melanoma and the selection of mutant alleles during progression

Background:Oncogenic BRAF mutation had been considered to be a founder event in the formation of melanocytic tumours; however, we recently argued against this notion by showing marked polyclonality of BRAF mutations in acquired melanocytic nevi (Lin et al, J Natl Cancer Inst., 2009; 101:1423–7). Here, we tested whether similar heterogeneity of BRAF mutations exists in primary melanomas.Methods:We isolated and sequenced single melanoma cells from five primary melanoma tissues using antibodies against human high-molecular-weight melanoma-associated antigen. We also examined 10 primary melanomas by the sensitive Mutector assay detecting the BRAFV600E mutation, as well as by cloning and sequencing of separated alleles. Furthermore, we estimated the frequency of BRAF mutant alleles in paired samples of primary tumour and recurrence or metastasis in three patients.Results:Single-cell mutation analyses revealed that four of five primary melanomas contained both BRAF-wild-type and BRAF-mutant tumour cells. Tumour heterogeneity in terms of BRAF mutations was also shown in 8 of 10 primary melanomas. Selection of BRAF mutant alleles during progression was demonstrated in all the three patients.Conclusion:Acquisition of a BRAF mutation is not a founder event, but may be one of the multiple clonal events in melanoma development, which is selected for during the progression.

Mutation analysis of BRAF and KIT in circulating melanoma cells at the single cell level

Background:The availability of molecular-targeted therapies for the treatment of melanoma has emphasised the need to identify mutations in target genes such as BRAF and KIT. Circulating tumour cells (CTC) are present in the peripheral blood of a significant proportion of cancer patients.Methods:High molecular weight melanoma-associated antigen (HMW-MAA) was used to isolate melanoma cells from peripheral blood as it is selectively expressed at high levels on melanomas. The HMW-MAA-positive cells were isolated using immunomagnetic beads. After removing CD45+ cells, CTC were identified by staining with MART-1- and gp100-specific antibodies (HMW-MAA+, CD45−, MART-1/gp100+). Single, isolated CTC were then subjected to BRAF and KIT mutational analysis.Results:CTC (HMW-MAA+, CD45−, MART-1/gp100+) were isolated from the blood of 11 patients and BRAF and KIT were sequenced in nine and four patients, respectively. The BRAF sequences identified in the CTC were inconsistent with those identified in autologous melanoma tumours in three patients and the KIT sequences were inconsistent in three patients. In addition, polyclonal BRAF mutations were identified in one patient and concomitant mutations in BRAF and KIT were identified in another patient.Conclusion:Melanoma cells show clonal heterogeneity. Therefore, CTC genotyping may be crucial for successful molecular-targeted therapy.

Clinical characteristics associated with BRAF, NRAS and KIT mutations in Japanese melanoma patients

BACKGROUND The importance of the genetic background of melanoma cells to the individual susceptibility to treatment has become apparent. In Caucasians, BRAF mutations are frequently detected in lesions on the skin of younger patients compared to NRAS and KIT mutations. However, clinical and pathological characteristics associated with BRAF, NRAS and KIT mutations have not been fully evaluated in East Asians. OBJECTIVE To clarify clinical and pathological characteristics associated with BRAF, NRAS and KIT mutations in Japanese melanoma patients. METHODS Clinical data were retrospectively collected from 11 hospitals in Japan. BRAF, NRAS and KIT mutations were evaluated with polymerase chain reaction and Sanger sequencing. The relationships between these gene mutations and pathological and clinical findings were analyzed. RESULTS The number of cases examined was 171 (primary: 135, metastases: 11, paired: 25), and all were Japanese patients. The detection rates of BRAF, NRAS and KIT mutations were 30.4%, 12.3% and 12.9%, respectively. Compared with the wild type, the presence of BRAF mutations was significantly associated with younger age (median, 50.0 years vs. 70.0 years, p<0.001). BRAF mutation was frequently detected in the lesions of the scalp (80%; 4/5), trunk (72.0%; 18/25), extremities (56.7%; 17/30) and neck (44.4%; 4/9), and the least prevalent were the face (22.2%; 2/9), nail (12.5%; 3/24), palm or sole (8.9%; 4/45) and mucosa (0%). NRAS mutations were prevalent in the face (33.3%) and palm or sole (20.0%), and the median age of these patients was 70.5 years. A KIT mutation was observed in the nail apparatus (25%), palm or sole (15.6%) and mucosa (18.2%). The median age of the patients with a KIT mutation was 63.0 years. Heterogeneity of mutations between primary and metastatic lesions was detected in six of 25 cases (24%). Solar elastosis was identified in 12 of 71 cases (15.3%), among which four cases harbored BRAF(V600E) (2 cases), BRAF(V600K), NRAS(Q61K) or NRAS(Q61L), respectively. CONCLUSION Some clinical characteristics associated with BRAF, NRAS and KIT mutations were observed in Japanese patients, and we observed both similarities to and differences from those of Caucasians. Our findings could provide useful information in efforts to clarify the tumor genesis of malignant melanomas.

5-Hydroxymethylcytosine is a useful marker to differentiate between dermatofibrosarcoma protuberans and dermatofibroma

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