How Do Long-Term Outcomes Differ Between Lobular Carcinoma and Breast Cancer of No Special Type?

Invasive lobular carcinoma (ILC) is the second most common type of breast cancer after breast cancer of no special type (NST), accounting for 10% to 15% of all new cases. Although differences in morphology, biological features, and clinical characteristics between these two subtypes have long been known, treatment approaches remain similar. Research is focused on understanding how these differences could be leveraged into developing better therapies for ILC. A key question is whether long-term outcomes differ between ILC and NST. Clinical trials usually include only a minority of patients with ILC; thus, statistical power to draw conclusions regarding differences in outcomes is often lacking.

These investigators combined data from 12,482 patients with axillary node-positive, early-stage breast cancer enrolled in four randomized, phase 3 trials of anthracycline-based adjuvant therapy. Compared with patients with NST (n=11,251), those with ILC (n=1231) were older (mean, 53.5 vs. 49.5 years), had bigger tumors (mean, 3.41 vs. 2.65 cm) and higher nodal burden (mean, 4.9 vs. 3.9), and were more likely to have estrogen receptor–positive (ER+) disease (89.7% vs. 67.3%) and undergo mastectomy (74.1% vs. 56.1%). Propensity-score matching yielded a final study cohort of 4694 patients with NST and 1174 with ILC.

During the first 5 years of follow-up, patients with ILC had lower rates of disease-free survival (DFS) events (hazard ratio, 0.83), recurrence (HR, 0.797), and death (HR, 0.756) than those with NST. However, after 5 years, patients with ILC had higher rates of DFS events (HR, 1.176), recurrence (HR, 1.30), and death (HR, 1.044). Differences in recurrence rates were not influenced by ER status.