Invasive lobular carcinoma (ILC) is the second most common histological subtype of breast cancer, after the more common invasive ductal carcinoma (IDC). ILC accounts for 10 to 15% of all invasive breast carcinomas, affecting approx. 26,000-40,000 women in 2020 in the US alone. Despite 95% of ILC being Luminal A conferring patients a favorable prognosis, patients with ILC have poorer long-term outcomes when compared to patients with Luminal A IDC. ILC spread to common sites of ER+ breast cancer metastasis such as the bones, but are also three times more likely to spread to the ovaries, peritoneum, and gastrointestinal tract compared to IDC, and these unique aspects of metastases remain poorly understood. To better understand metastasis to the ovary we performed DNA and RNA sequencing of 11 pairs of primary breast tumor and ovarian metastasis as well as 13 orphan breast cancer ovarian metastases. Our cohort was enriched for lobular histology, with 13 samples originating from ILC, 6 from IDC and 6 from mixed ILC/IDC. We found mutations in CDH1 (43%), PIK3CA (40%), and FOXA1 (29%) highlighting the enrichment in ILC cases present in our cohort. Gene expression analysis lead to identification of 874 differentially expressed between primary tumors and ovarian metastases. We identified the calcium-sensing receptor CaSR as one of the top upregulated in ovarian metastases compared to primary tumor in 10 out of the 11 paired samples. Other genes highly expressed in ovarian metastases included TAC3, GLRA2, ALLC, MUC19, CHRNA2, PIP, CST4, and TEX15. Pathways analyses showed an enrichment of signaling through glutamate receptor and glycine receptor families. To assess the contribution of CaSR to breast cancer cell proliferation and metastatic properties, and due to the absence of breast cancer cell lines expressing CaSR, we generated CaSR overexpression models using lentiviral infection in MDA-MB-134, MDA-MB-330, BCK4 and SUM44PE ILC cell lines. While overexpression of CaSR alone did not confer a cell growth advantage or migratory ability to the cell lines, stimulation with calcium or a calcium mimetic resulted in enhanced migration in transwell assays in 3 of the 4 cell lines. Scratch assays further confirmed the stimulation of cell migration in cells with CaSR overexpression in the presence of calcium. Cell migration in CaSR overexpression models could be stimulated with the calcimimetic R568, and inhibited by the calcilytics NPS2143, and F-actin staining confirmed the need to activate the receptor to enhance migratory properties. Our studies further revealed that the induced migratory properties of CaSR overexpressing cells required estradiol and ER signaling, and that migration could be blocked with ER inhibitors such as ICI 182,780 and tamoxifen. Western blotting data revealed that the enhanced cell migratory properties of CaSR overexpressing cells was via activation of the MEK/ERK pathway and migration could be inhibited using specific small molecule pathway inhibitors.Altogether, our study provides insight on the potential mechanism by which upregulation of the CaSR supports breast cancer ovarian metastasis. We hope that these studies will not only deepen our understanding of ILC ovarian metastasis but will eventually lead to the development of more effective therapies and improve the outcome of patients with this understudied type of breast cancer.

Citation Format: Ye Qin, Laura Savariau, Ahmed Mohammed Basudan, Osama Shah, Zheqi Li, Tiantong Liu, Nilgun Tasdemir, Lan Coffman, Esther Elishaev, Jennifer M Atkinson, Peter Lucas, Adrian V Lee, Steffi Oesterreich. Role of the calcium-sensing receptor (CaSR) in invasive lobular breast carcinoma metastasis to the ovary [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS19-06.