LAUSR

BACKGROUND: Endometriosis affects ~10% of reproductive–aged women and is characterized by extra–uterine biphasic growth of uterine endometrial epithelium and stroma. Endometriosis is widely considered to be a hormonally–dependent inflammatory condition and is classified into three anatomically defined types: deep infiltrating endometriosis that locally invades pelvic organs; ovarian endometriotic cysts, and superficial peritoneal endometriosis. A clonal “precursor–cancer” link to co–occurring clear cell and endometrioid ovarian cancers has been established and somatic mutations occur in these cancer–associated endometriotic cysts, including distant benign–appearing lesions. The spectrum of genetic alteration in non–cancer associated endometriosis is not known. METHODS: We screened a pilot series of 10 deep–infiltrating [pelvic] endometriosis lesions, without co–occurrence or history of cancer, for somatic alterations using laser captured endometrial stroma and epithelium. Two overlapping amplicon panels and digital PCR were used to validate mutations. RESULTS: In four of ten cases we validated the presence of activating codon 12 KRAS mutations. Mutations were restricted to the epithelium and no evidence of any alterations was found in the stromal fraction. CONCLUSIONS: We provide incontrovertible evidence of activating KRAS mutations in 40% of deep infiltrating endometriosis. This frequency of KRAS mutations is substantially higher than what has been observed in clear cell (CCOC) or endometrioid (ENOC) ovarian cancers and the occurrence of non–ovarian primary CCOC/ENOC is largely anecdotal. Our evidence suggests that these mutations represent core features of endometriosis itself, rather than a risk of malignant transformation. Overall we propose this as an opportunity to fundamentally shift the study of endometriosis to a spectrum of neoplasms. This may lead to the generation of a molecularly informed classification system and ultimately to improved prognostication and treatment. Citation Format: Michael S. Anglesio, Tayyebeh M. Nazeran, Hugo M. Horlings, Vivian Lac, Amy Lum, Janine Senz, Julie Ho, Amy Wang, Fontayne Wong, Catherine Allaire, Christina Williams, C. Blake Gilks, Paul J. Yong, and David G. Huntsman. GENOMIC ALTERATIONS IN ENDOMETRIOSIS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr AP09.