Search

Biology and transcriptomes of non-cancerous human mammary epithelial cells at risk for breast cancer development were explored following primary isolation utilizing conditional reprogramming cell technology from mastectomy tissue ipsilateral to invasive breast cancer. Cultures demonstrated consistent categorizable behaviors. Relative viability and mammosphere formation differed between samples but were stable across three different mammary-specific media. E2F cell cycle target genes expression levels were positively correlated with viability and advancing age was inversely associated. Estrogen growth response was associated with Tissue necrosis factor signaling and Interferon alpha response gene enrichment. Neoadjuvant chemotherapy exposure significantly altered transcriptomes, shifting them towards expression of genes linked to mammary stem cell formation. Breast cancer prognostic signature sets include genes that in normal development are limited to specific stages of pregnancy or the menstrual cycle. Sample transcriptomes were queried for stage specific gene expression patterns. All cancer samples and a portion of high-risk samples showed overlapping stages reflective of abnormal gene expression patterns, while other high-risk samples exhibited more stage specific patterns. In conclusion, at-risk cells preserve behavioral and transcriptome diversity that could reflect different risk profiles. It is possible that prognostic platforms analogous to those used for breast cancer could be developed for high-risk mammary cells.

An intervention study initiated at age 4 months compared the impact of tamoxifen (25mg), raloxifene (22.5mg) and letrozole (2.5mg) administered by 60-day-release-subcutaneous-pellet on mammary preneoplasia prevalence at age 6 months in conditional genetically engineered mouse models with different Brca1 gene dosages targeted to mammary epithelial cells and germline Trp53 haploinsufficiency (10-16/cohort). The proportion of unexposed control mice demonstrating mammary preneoplasia at age 6 months was highest in Brca1fl11/fl11/Cre/p53−/+ (54%) mice followed by Brca1WT/fl11/Cre/p53−/+ mice (30%). By age 12 months invasive mammary cancers appeared in 80% of Brca1fl11/fl11/Cre/p53−/+ and 42% of Brca1WT/fl11/Cre/p53−/+ control unexposed mice. The spectrum of cancer histology was similar in both models without somatic mutation of the non-genetically engineered Brca1, Trp53, Brca2 or Dapk3 alleles. Two months exposure to tamoxifen, raloxifene and letrozole significantly reduced estrogen-mediated tertiary branching by 65%, 71% and 78%, respectively, in Brca1fl11/fl11/Cre/p53−/+ mice at age 6 months. However, only letrozole significantly reduced HAN prevalence (by 52%) and number (by 30%) and invasive cancer appeared despite tamoxifen exposure. In contrast, tamoxifen significantly reduced HAN number by 95% in Brca1WT/fl11/Cre/p53−/+ mice. Control mice with varying combinations of the different genetically modified alleles and MMTV-Cre transgene demonstrated that the combination of Brca1 insufficiency and Trp53 haploinsufficiency was required for appearance of preneoplasia and no individual genetic alteration confounded the response to tamoxifen. In summary, although specific antihormonal approaches showed effectiveness, with Brca1 gene dosage implicated as a possible modifying variable, more effective chemopreventive approaches for Brca1-mutation-induced cancer may require alternative and/or additional agents.