Abstract P1-21-03: Unique estrogen receptor alpha turnover, regulation and targeting in invasive lobular breast carcinoma

Invasive lobular breast carcinoma (ILC) accounts for 10-15% of breast cancers diagnosed annually. Evidence suggests that endocrine treatment response might differ between invasive ductal carcinoma (IDC) and ILC, and that patients with ILC have worse long-term survival. ILCs are more likely to be estrogen receptor alpha (ER/ERα) positive (90-95%) compared to IDCs (60-70%). We investigated whether there are differences in ER protein steady state levels and/or turn-over rates in ILC that might explain differences in response to endocrine therapy. Analysis of the TCGA dataset revealed lower levels of ESR1 mRNA (P = 0.002) and ERα protein (P = 0.038) in ER+ ILC (n = 137) compared to ER+ IDC (n = 554). Supporting this observation, analysis of tumors from patients treated at UPMC Magee-Women’s Hospital (ILC, n = 143; IDC, n = 877), showed lower ESR1 mRNA (P Citation Format: Jennifer M Atkinson, Sreeja Sreekumar, Kevin M Levine, Matthew J Sikora, Jian Chen, David J Dabbs, Carolin Meier, Ahmed Basudan, Nilgun Tasdemir, David Boone, Priscilla F McAuliffe, Rachel C Jankowitz, Adrian V Lee, Steffi Oesterreich. Unique estrogen receptor alpha turnover, regulation and targeting in invasive lobular breast carcinoma [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-21-03.