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Implications of BRCA-loss phenotype in epithelial ovarian carcinoma Press, Joshua Zephyr

Abstract

Loss of BRCA1/BRCA2 function through genetic or epigenetic mechanisms is common in epithelial ovarian carcinomas (EOC), but because there are multiple potential mechanisms of loss, the overall frequency is unknown. We characterized loss of BRCA1/BRCA2 at the DNA, RNA and protein level from an unselected, consecutive series 49 non-mucinous, invasive EOC. BRCAl-loss was found in 21/49 tumors (43%). These included 8 tumors from patients with BRCA1 germline mutations, 1 tumor with a somatic BRCA1 mutation and 12 tumors (24%) that showed BRCAl-loss without evidence of BRCA1 mutation. Three tumors that contained BRCA2 mutations (2 germline/1 somatic) did not exhibit BRCAl-loss. The histopathology of the tumors showing BRCAl-loss was high-grade serous or undifferentiated carcinoma in every case (even in the absence of mutations) with 21/38 high-grade serous/undifferentiated EOC showing BRCAl-loss. None of the 11 tumors of non high-grade serous type (5 endometrioid, 4 clear cell, and 2 low-grade serous) exhibited BRCAl-loss. High-grade serous/undifferentiated EOC with BRCAl-loss showed different immunophenotype compared to those without BRCAl-loss (p53+, p21-, cyclin D1-). Progress in the treatment of EOC requires appropriate in vivo models to assess novel targeted therapeutic agents, such as the ability of Poly(ADP-ribose) polymerase (PARP) inhibitors to selectively damage BRCAl-null tumor cells. We evaluated the genetic/phenotypic stability of primary human gynecological tumors grown as serially transplanted xenografts in NOD/SCID mice. Transplantable tumor lines were derived from 5 tumors, and serially transplanted for 2-6 generations. Comparisons were made between primary tumor and corresponding transplantable xenografts. Genetic stability was suggested by unsupervised hierarchical cluster analysis of a 287 feature comparative genomic hybridization array. Phenotypic stability was suggested by immunohistochemistry using antibodies against EGFR, HER2, HER3, IGF-IRp, Mucinl, E-cadherin, P-catenin, and VEGF. Analysis of a xenograft from a patient with a known germline BRCA1 mutation confirmed the presence of a hemizygous truncating mutation within BRCA1 exon2 (del 185AG), associated with loss of heterozygosity (LOH). Another case had no mutations in BRCA1, but showed LOH and promoter hypermethylation, with undetectable BRCA1 protein, indicating epigenetic loss. These models may be used to assess targeted therapeutics, such as PARP inhibitors in tumors with genetic or epigenetic BRCAl-loss.

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