Abstract P6-03-14: Expression of genes for aromatase inhibitor targets to discriminate invasive lobular from invasive ductal carcinomas of the breast using LCM-procured cells to complement endocrine biomarkers
Authors: Sanders MAG , Daniels MW , Wittliff JL 
Published: May 2016

Background: The BIG 1-98 trial and later the ABCSG 8 study reported that patients with invasive lobular carcinoma (ILC) exhibited better response to aromatase inhibitors (AIs) compared to those with invasive ductal carcinoma (IDC). Aromatase cytochrome P450 (CYP19) synthesizes estrogen from androgens and is the target of AI's. CYP19 substrates are generated by upstream enzymes including estrone sulfatase (SULT1E1) and 3b-hydroxysteroid dehydrogenase type 1 (HSD3B1). Enzymes of the aromatase pathway have been reported to be expressed in intact tissue biopsies of breast cancer. To learn more about the pathogenic mechanisms that may underlie the survival benefit of ILCs treated with AIs, we analyzed expression levels of key enzymes related to the aromatase pathway in ILC and IDC. Unlike previous studies, we determined gene expression levels directly on pure populations of carcinoma cells procured by laser capture microdissection, eliminating the contribution of non-cancerous cells.

Methods: Using an IRB-approved biorepository and database, total RNA was extracted from carcinoma cells of 247 de-identified biopsies to perform microarray analyses of 22,000 genes. Of the 247 samples, 16 were ILC, 13 were low grade IDC, 55 were intermediate grade IDC and 85 were high grade IDC, and 107 of these were hormone receptor positive. CYP19, HSD3B1 and SULT1E1 expression was directly detected in LCM-procured breast carcinoma cells of ILC and of IDC. Expression of other genes generally associated with the aromatase pathway, e.g., NADPH-cytochrome P450 reductase (POR), ATP-binding cassette gene (ABCG2), catechol-o-methyltransferase (COMT) and uridine-5'-diphosphate glucuronosyltransferase (UGT1A3 & UGT1A9) as well as HSD17B2 were assessed with LCM-procured cells. Estrogen receptor (ER) and progesterone receptor (PR) proteins were quantified by radio-ligand binding and EIA, and gene expression was validated by qPCR.

Results: Univariate Cox regression analyses indicated that ABCG2, HSD17B2and UGTA3 independently predicted disease free and/or overall survival of breast carcinomas. We found that CYP19 expression in carcinoma cells, as well as SULT1E1, COMT, POR, HSD17B2 and UTG1A3 expression, decreased as either ER or PR protein increased. HSD3B1 appeared to be over-expressed in ILC compared to IDC, however this difference did not approach statistical significance, likely due to the small sample size. No differences were seen in expression levels of CYP19 and SULT1E1 between ILC and IDC.

Conclusions: An inverse relationship between CYP19 and ER and PR expression levels was observed and suggests that synthesis of estrogens by breast cancer cells in situ plays a significant role in defining tumor biology. Our results also indicate overexpression of HSD3B1 in ILC, although not statistically significant. This finding suggests that HSD3B1 may be a key contributor to the increased benefit of AI therapy seen in ILC. Collectively our results suggest a comprehensive study is warranted to ascertain the molecular basis for differences in expression of genes directing estrogen synthesis in situ in relationship to AI therapeutic responses of histologic subtypes of breast carcinomas.

Citation Format: Sanders MAG, Daniels MW, Wittliff JL. Expression of genes for aromatase inhibitor targets to discriminate invasive lobular from invasive ductal carcinomas of the breast using LCM-procured cells to complement endocrine biomarkers. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-03-14.