Evaluating Surgical Outcomes Between Estrogen Receptor Positive Invasive Lobular and Invasive Ductal Carcinoma of the Breast-A Propensity Matched Analysis.

About 762 cases of ER + breast cancer have been included in this analysis of the influence of histological subtype on long-term outcomes in breast cancer. Following rigorous propensity matching, cases of ILC have been compared to IDC and demonstrate, better long-term survival in the ILC cohort. ILC cases are also more likely to undergo mastectomy and less likely to undergo neoadjuvant chemotherapy. Introduction: Invasive lobular carcinoma (ILC) contributes significantly to the global cancer burden and is the most common of the histological "special types" of breast cancer. ILC has unique features setting it apart from the more common invasive ductal carcinoma (IDC). Despite differences, treatment algorithms do not consider histological differences. Aim: To determine the differences in treatment and outcomes of ILC relative to IDC in a strict case-matched cohort study at a tertiary referral, specialist, breast cancer center. Methods: All Estrogen receptor positive (ER + ) ILCs from 1999 to 2015 were matched for; age, tumor size, grade, PR/HER2 status, nodal stage and metastases with ER + IDCs from the same period. Surgical and systemic treatments were assessed along with overall (OS) and disease-free survival (DFS). Results: 762 cases in total were analyzed (1:1 matching; ILC:IDC). ILC cases were more often treated with mastectomy (37.5% vs. 28.6%, P .009) and those who received breast conserving surgery (BCS) more often had an incomplete resection (30.2% vs. 19.6%, P .01). IDC were more often treated with NACT (5.5% vs. 14.4%, P < .001). Mean DFS were similar between ILC and IDC; 148.3 vs. 141.4 months ( P .112) but OS was significantly longer in the ILC group; 165.7 vs. 134 months ( P .002). This trend was consistent among the subset of patients undergoing BCS. For ILC undergoing BCS, mean DFS was 129.8 vs. 128.3 months for IDC ( P .418) and OS was 155.4 and 110.7 months respectively ( P < .001). Incomplete resection at the time of index surgery did not alter the disease free or overall survival in either the ILC or IDC patients to a level that reached statistical significance. Conclusion: In this cohort study, the strict matching of ILC and IDCs for a number of prognostic indicators, demonstrates the impact of lobular histology with a clarity not previously observed. ILCs have comparable survival outcomes to patients with IDC but at the expense of more extensive index and revisional surgery. There is a need for awareness of these facts among surgeons and patients for optimal treatment prioritization and provision.