Abstract 4854: Mutations activating proliferation pathways in ovarian cancer

Abstract

Abstract Ovarian malignancies may arise through different mechanisms of oncogenesis, which influence their treatment and are important for prognosis. Essential to carcinogenesis is the activation of proliferation pathways such as those directed by PI3 kinase or KRAS. New sequencing technologies may improve the detection of somatic mutations in tumor tissue, which is complicated by the low representation of a mutation within a tissue sample inevitably containing normal cells and subpopulations of malignant cells. We analyzed selected exons in PIK3CA, PIK3R, KRAS, BRAF, EGFR and ERBB2 in 34 primary malignant ovarian tumors, including 10 serous, 4 borderline, 11 endometrioid, and 9 mixed or rare subtypes. DNA was extracted from flash-frozen tumor tissues, amplified, and sequenced on a 454-GS-Flx Genome Sequencer. Expression of PTEN, p53, Bcl2, ALDH and Ki67 were assessed by immunohistochemistry on formalin-fixed tissues. Nine mutations were observed in PIK3CA, 5 in BRAF, 4 in KRAS, and 2 in EGFR. SNPs present in the amplicons analyzed allowed allelic imbalance to be estimated, showing possible amplification of EGFR in 9 of 20 informative samples, and of PIK3CA in 6 of 19 informative samples, none of which contained a point mutation. Endometrioid tumors frequently showed anomalies in PIK3CA, Bcl2 expression, and not p53 overexpression. P53 overexpression was typical of serous tumors, and was associated with the absence of mutations in any of the genes sequenced. Borderline and low grade tumors were characterized by BRAF mutation, no imbalance at EGFR, no anomalies at PIK3CA, and less frequent p53 overexpression. The absence of BRAF mutations in high grade tumors suggested that they do not evolve from borderline tumors. PIK3CA mutations were not mutually exclusive with KRAS mutations, confirming the non-redundancy of these intertwined signaling pathways. PTEN extinction was not significantly negatively associated with either point mutations or allelic imbalance at PIK3CA, consistent with different roles for PTEN loss and PI3-kinase activation at different stages of tumorogenesis, in spite of the close association of PTEN with the PI3-kinase pathway. No significant associations were observed between ALDH and Ki67 and any parameters measured. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4854. doi:10.1158/1538-7445.AM2011-4854