Introduction: Invasive lobular breast cancer (ILC) is the second most common subtype of invasive breast cancer accounting for 10% of breast cancer diagnosis. ILC has particular histological and clinical characteristics and a distinct response to therapy. Characterizing the molecular alterations in ILC may lead to an improved understanding of its biology and provide new therapeutic options. The purpose of this study is to describe the molecular profile of ILC and compare it to the one of invasive ductal cancer (IDC).

Methods: Three-hundred and thirty nine pure ILC specimens profiled from January 2012 - November 2015 were evaluated (Caris Life Sciences, Phoenix, AZ). Multiplatform profiling consisted of gene sequencing (next generation sequencing [NGS]), gene amplification (CISH or FISH), and protein expression (immunohistochemistry [IHC]). Molecular characteristics of estrogen receptor (ER) positive and human epidermal growth receptor factor 2 (HER2) negative pure ILC (n = 236) and IDC (n = 286) were compared.

Results: By IHC, ER expression was present in 87.7% (277/316), progesterone receptor in 59.6% (198/313), HER2 in 3.5% (11/313), androgen receptor in 87% (262/301), PD-L1 in 8.1% (12/148) and PTEN in 63.3% (198/313). Amplifications were detected in MYC (7.7%, 2/26), EGFR (8.3%, 2/24), ERBB2 (4.5%, 13/290) and TOP2A (1.3%, 3/236). Mutations were detected in AKT1 (4.7%, 9/191), ATM (3.7%, 7/190), BRCA1 (4.2%, 4/96), BRCA2 (9.5%, 9/95), ERBB2 (7.5%, 14/186), PIK3CA (54.5%, 103/189), PTEN (7.9%, 15/189), and TP53 (13.4%, 25/186). A comparison of ER-positive/HER2-negative invasive lobular and ductal carcinomas revealed significant differences in AR expression (89.7% vs 79.6%, p = 0.0022), and mutations in CDH1 (10.1% vs 0.0%, p = 0.0001), ERBB2 (8.2% vs 2.1%, p = 0.0079), and TP53 (10.3% vs 31.8%, 0.0001).

Conclusions: Multiplatform testing of this large series of ILC reveals recurrent alterations and a distinct molecular profile when compared to IDC. These support the definition of ILC as biologically distinct entity. High AR expression and high rates of dysregulation along the PIK3CA/AKT/mTOR pathway are consistent with recent reports in the literature.

Citation Format: Raquel A. Nunes, David Arguello, Zoran Gatalica, Sandeep Reddy, Sandra M. Swain. Multiplatform molecular profiling of invasive lobular breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 123.

©2016 American Association for Cancer Research.
2016
American Association for Cancer Research.