Invasive lobular carcinoma (ILC) is the second most common histologic breast cancer subtype and represent approximately 10% of all breast cancers. Despite this high frequency, benefit of adjuvant chemotherapy (CT) in ILC is still unclear.
Our objective was to investigate the impact of CT on survival in ILC. Patients were retrospectively identified from a cohort of 23,537 patients who underwent primary surgery in 18 French centres between 1990 and 2014. Only ILC, hormone-positive, HER2-negative patients who received adjuvant endocrine therapy (ET) were included. Endpoints were disease-free survival (DFS) and overall survival (OS). A propensity score for receiving CT was estimated using a logistic regression including age, tumour size, nodal status, lymphovascular invasion (LVI), grade, type of surgery, period and CT.
Of a total of 2,318 patients with ILC, 1,485 patients (64%) received ET alone and 823 (36%) received ET+CT. Patients receiving ET+CT had more adverse prognostic features, such as young age, larger tumour size, high grade, macroscopic lymph-node involvement and LVI, received more adjuvant radiotherapy and underwent more often mastectomy. In a multivariate Cox model, we observed a beneficial effect of addition of CT to ET on both DFS and OS, (HR = 0.61, 95% CI [0.41-0.90]; p = 0.01 and 0.52, 95% CI [0.31-0.87]; p = 0.01, respectively). This effect was even more pronounced when propensity score-matching, aiming to compensate for baseline characteristics, was used. Ten-year estimates DFS in case-matched patients for propensity score analysis were 90% (95% CI [87%-93.4%]) in the ET+CT group vs. 66% (95% CI [61.4%-71.4%]) with ET alone and 10-year estimates OS were 96% (95% CI [93.8%-98%]) in the ET+CT group vs. 71% (95% CI [66.6% et 76.2%]) with ET alone. Regarding subgroup analysis, low-risk patients without CT did not have significant differences in DFS or OS compared to low-risk patients with CT.
Patients receiving adjuvant ET for hormone receptor-positive, HER2-negative ILC could derive significant DFS and OS benefits from CT. Our results highlight that patients with high-risk ILC should not be denied adjuvant CT because of such histologic subtype.
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All authors have declared no conflicts of interest.