Frequency of BRAF V600E variant in circulating free DNA compared with the single melanoma biopsy

9092

Background: To select melanoma patients for treatment with BRAF inhibitors, the BRAF mutational status is determined in the most recent tumor biopsy. However, tumor specimens are not always available for the analysis, and relying on a single biopsy specimen can potentially exclude from treatment patients with heterogeneity among metastatic tumors due to polyclonality of BRAF mutation, which appears as a rather common condition. As an alternative approach we explored a blood-based mutation detection assay. Methods: We developed a method including enrichment for the BRAV600E variant by selective elimination of the wild type allele by TspRI digestion and BRAFV600E detection by TaqMan Mutation Detection Assay (BRAF_476_mu, Life Technologies). Sensitivity testing showed that BRAFV600E variant was detected starting from 6.25X10-5 ng of DNA, and specificity testing showed that the variant can be detected when diluted in 8X105 copies of wild-type alleles. Results: Mutational analysis performed by Sanger sequencing of exon15 in 114 melanoma biopsies showed that 4 (3%) harbored the c.1798_1799GT>AA (V600K) mutation, 1 (1%) the c.1799_1800TG>AA mutation (V600E), and 56 (49%) the most common c.1799T>A mutation (V600E), while by the novel method the latter mutation was detected in 9 additional specimens (8% increment) and confirmed by sequencing the PCR product after TspRI digestion. Pre-surgery plasma was available for 50/114 patients at advanced stages, 26/50 (52%) showing a mutated specimen, including 4 with a double nucleotide substitution (V600K and V600E). The matched plasma samples resulted mutated in 25/26 cases with mutated biopsy and in further 14/25 samples with biopsy resulting wild type; in contrast, plasma of 50 healthy controls tested negative. Taken together, these results indicate that V600E circulating variant was detectable in 39/50 (78%) plasma samples and in 22/50 (44%) tumor specimens. Conclusions: Detection of BRAF V600E variant in circulating free DNA may represent a more sensitive approach for patient selection and decision making process during the treatment with BRAF inhibitors.

Limited induction of tumor cross-reactive T cells without a measurable clinical benefit in early melanoma patients vaccinated with human leukocyte antigen class I-modified peptides

PURPOSE

The progressive immune dysfunctions that occur in patients with advanced melanoma make them unlikely to efficiently respond to cancer vaccines. A multicenter randomized phase II trial was conducted to test whether immunization with modified HLA class I tumor peptides in the context of adjuvant therapy results in better immunologic responses and improved clinical outcomes in patients with early melanoma (stages IIB/C-III).

EXPERIMENTAL DESIGN

Forty-three patients were enrolled to undergo vaccination (n = 22) or observation (n = 21). The vaccine included four HLA-A*0201-restricted modified peptides (Melan-A/MART-1([27L]), gp100([210M]), NY-ESO-1([165V]), and Survivin([97M])) emulsified in Montanide ISA51 and injected subcutaneously in combination with cyclophosphamide (300 mg/m(2)) and low-dose IL-2 (3 × 10(6) IU). The immune responses were monitored using ex vivo IFN-γ-ELISpot, HLA/multimer staining, and in vitro short-term peptide sensitization assays.

RESULTS

Vaccination induced a rapid and persistent increase in specific effector memory CD8(+) T cells in 75% of the patients. However, this immunization was not associated with any significant increase in disease-free or overall survival as compared with the observation group. An extensive immunologic analysis revealed a significantly reduced cross-recognition of the corresponding native peptides and, most importantly, a limited ability to react to melanoma cells.

CONCLUSIONS

Adjuvant setting is an appealing approach for testing cancer vaccines because specific CD8(+) T cells can be efficiently induced in most vaccinated patients. However, the marginal antitumor activity of the T cells induced by modified peptides in this study largely accounts for the observed lack of benefit of vaccination. These findings suggest reconsidering this immunization strategy, particularly in early disease.