PhD Scientific Days 2018

Budapest, April 19–20, 2018

Alteration of mutant allele frequency is significant in visceral metastases of melanoma

Doma, Viktória

Viktória Doma MD 1,2 Orsolya Papp MSc 2, Erzsébet Rásó MSc, PhD 2, Tamás Barbai MSc 2, PhD, Lilla Reiniger MD, PhD 3,4, Laura Vízkeleti MSc, PhD 2,4, József Tímár MD, PhD, DSc 2,4,5
1: Department of Dermatology, Venerology and Dermatooncology, Semmelweis University, Budapest, Hungary
2: 2nd Department of Pathology, Semmelweis University, Budapest, Hungary
3: 1st Department of Pathology and Experimental Cancer Research, Semmelweis University, Budapest, Hungary
4: Brain Metastasis Research Group, Hungarian Academy of Sciences and Semmelweis University, Budapest Hungary
5: Molecular Oncology Research Group, Hungarian Academy of Sciences and Semmelweis University, Budapest Hungary

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Text of the abstract

Metastatic drivers in melanomas are in focus of translational research.
50 patients were collected with primary skin melanomas and 139 corresponding visceral metastases at autopsy. Oncogenic driver mutations were determined by Sanger- and pyrosequencing. Mutant variant allele frequencies (MAF) were re-calculated compensating for tumor/normal cell ratio. Chromosome Analysis Suite 3.3. was used for cytognetic analysis underlying BRAF/NRAS MAF alterations.
BRAF, NRAS and KIT mutations were found at 64%, 24% and 0%, respectively. In case of BRAFmut/NRASmut tumors CNS was the most frequent metastases, followed by lung in BRAFmut and liver in NRASmut tumors. MAF increased significantly in metastases compared to primaries in BRAFmut tumors exclusively which was due to significant increase in lung- and less common metastases. Based on MAF values mutant alleles were classified as heterozygous-monoclonal (>40%), polyclonal (15-40%) or subclonal (<15%). Interestingly, both oncogenic drivers MAF values were <50% in the majority of the primary tumors (41/44=93,2%). Stability of the MAF value is characteristic of NRASmut melanoma (6/12=50%) unlike in BRAFmut tumors (10/32=31.3%) where increase in MAF is the most frequent genetic event (18/32=56.3%). Almost third of primary melanomas (14/44=31,8%) contains one subclonal driver mutation. Increased MAF in metastases of BRAFmut tumors was most frequently accompanied by single copy increase of BRAF (polysomy). In lung metastases true BRAF gene amplification were detected. In NRASmut tumors the most frequent genetic alteration is LOH of various chromosomal regions, especially in liver metastasis. NRAS gene was diploid in primaries and metastases.
MAF can change unpredictably in metastases. Decrease in MAF is a rare event during visceral metastatic progression and is independent from oncogenic drivers. We suggest to characterize driver status of metastases rather than primaries before clinical decision making. It is clinically relevant to provide MAF values in the molecular report.
This work is supported by NKFI-K-112371, NVKP-16-1-2016-0004, NAPB/KTIA13-0021 and ÚNKP-17-3-III-SE-7.

Data of the presenter

Doctoral School of Pathological Sciences
Program: Experimental Oncolog
Supervisor: József Tímár