Opening the Door for Immune Oncology Studies in Invasive Lobular Breast Cancer

Invasive lobular breast cancer (ILC) is the second most common histological breast cancer subtype, after invasive ductal breast cancer (IDC). ILC accounts for approximately 10% to 15% of all breast cancers, with approximately 24 000–36 000 cases annually in the US only. The hallmark of ILC is loss of E-cadherin (CDH1), resulting in discohesive cancer cells that infiltrate the breast stroma in a single-file pattern (1). Unique clinical features that differentiate ILC from IDC include more frequent multifocal disease, growth patterns often resulting in higher stage at presentation, positive resection margins necessitating completion mastectomy (2–5), and metastatic sites (6,7). Despite better prognostic factors (eg, more estrogen receptor [ER]+, and lower levels of the proliferation marker Ki67), there is increasing evidence that patients with ILC have worse long-term outcome compared with those with IDC (8–10). Finally, recent studies by The Cancer Genome Atlas (TCGA) (11) and Rationale Therapy for Breast Cancer (12) consortia have demonstrated differences between the genetic make-up of ILC and IDC and—of relevance here—have consistently identified an "immune-related" ILC transcriptomic subtype.

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