Is There a Role for Oncotype Dx Testing in Invasive Lobular Carcinoma?

Oncotype Dx Breast Cancer Assay is a 21-gene assay used in estrogen receptor (ER)-positive breast cancer to predict benefit from chemotherapy (CT). Tumors are placed into one of three risk categories based on their recurrence score (RS). This paper explores the impact of tumor histopathologic features and Oncotype Dx RS on the treatment plan for invasive lobular carcinoma (ILC). Invasive lobular carcinoma cases submitted for Oncotype Dx testing were identified from a clinical data base. The histopathologic and immunohistochemical features and RS subcategory of each tumor, and treatment regimen and medical oncologic assessments of each patient were reviewed. A total of 135 cases of ILC had RS testing, which represented 15% of all ILC diagnosed at the institution over the time period. 80% of ILC was of the classical subtype and all tumors were ER positive and human epidermal growth factor receptor 2 (HER-2) negative by immunohistochemistry. Sixty three percent of cases were low risk (LR), 35.5% were intermediate risk (IR) and 1.5% were high risk (HR). Both HR cases were pleomorphic ILC. Sixty eight percent of classical ILC had a LR score, while 70% of pleomorphic ILC had an IR score. Patients in the IR category were significantly more likely to undergo CT than patients in the LR category (54% versus 18%; p<0.0001). In the LR category, those undergoing CT were significantly younger and more likely to have positive lymph nodes (p<0.05). Qualitative analysis of medical oncologic assessments showed that RS played a role in decision-making on CT in 74% of cases overall. At our institution, Oncotype Dx RS currently plays a role in the management of a proportion of ILC and impacts on treatment decisions.