Abstract P3-04-11: Thyroid hormone up-regulates estrogenic and pro-carcinogenic signaling, inducing a basaloid and more motile phenotype in only steroid receptor positive breast cancer cells

Background: Co-morbidity of thyroid disease and breast cancer has been recognized for over a century. Up to two-thirds of women with breast cancer have clinical or occult thyroid disease, as compared to one fifth of unaffected females. Thyroid disease typically proceeds breast cancer by at least a decade, and many (nearly half) are on long term thyroid hormone supplementation at the time of diagnosis. The exogenous administration of thyroid hormone, for hypothyroidism or status post thyroidectomy for neoplasia, has been associated with an increased risk of breast cancer and in some studies, a worse prognosis. Causality, however, has been controversial. Results: We studied over 800 consecutive node negative invasive breast cancer patients diagnosed between 1976 and 1993 from a single institution. Of these, 92% were chemo-naive and only 14% received tamoxifen, reducing interactions with treatment for the study design. We showed untoward significant interactions with both univariate and multivariate analyses, between thyroid hormone supplementation, disease free and disease specific survival only in patients with steroid receptor positive tumors. These interactions were strongest in pre-menopausal, as compared to post-menopausal patients. We thus hypothesized that thyroid hormone (TH), either indirectly or directly, promoted carcinogenesis via the steroid receptors (SR) for estrogen and/or progesterone and have interrogated mechanisms of these interactions in vitro. Estrogen (E2) induce significant cellular proliferation, whereas TH alone (at concentrations of T4 1 x 10-6:T3 at 2.5 x 10-7 M) induced only mild cell proliferation in SR+ (MCF-7 andT47D), but not SR- breast cancer cell lines (MDA-MB-468 and SKBR3). In contrast, TH induced significant proliferation in SR + cells at significantly lower doses (down to T4 1 x 10-12: T3 2.5 x 10-13 M) if administered with low dose estrogen (E2: 1 x 10 -10). These mitogenic effects were demonstrated by MTS and DNA quantification assays, as well as flow cytometry, which revealed the induction of G2/M arrest and an increase in the percentage of cells in S phase with TH alone (at higher doses) or TH + E2 (at lower doses). Tamoxifen partially mitigated the pro-growth effects of TH + E2, whereas ICI 182,780 completely abrogated these effects. Using Western blots we have shown that that TH (with or without E2) upregulated ERa expression and activation, Cyclin A, B,D1, and E, E2F1, MAPK/ERK1/2 but not AKT signaling. TH +/- E2 also promoted clonogenicity, motility, a more basal phenotype (CD24+/CD44+) and mammosphere formation in cells grown under non-adherent conditions. Conclusions: We have demonstrated in Stage I breast cancer patients with minimal systemic treatment, that the administration of TH was associated with a significantly shortened disease free and disease specific survival, only in patients whose tumors expressed SR. TH administered to SR+ cell lines, particularly when co-administered with E2 at therapeutic/physiologic doses, upregulates and activates ER, cell proliferation, a more aggressive and motile basaloid phenotype. Citation Format: Ann D Thor, Zeying Fan, Reema Wahdan-Alaswad, Susan M Edgerton. Thyroid hormone up-regulates estrogenic and pro-carcinogenic signaling, inducing a basaloid and more motile phenotype in only steroid receptor positive breast cancer cells [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-04-11.