Long-term outcomes by lobular vs ductal histology in 4 National Surgical Adjuvant Breast and Bowel Project adjuvant breast cancer trials.

We evaluated differences in long-term outcomes of invasive lobular carcinoma vs breast cancers of no special type treated with anthracycline-based adjuvant chemotherapy using 4 National Surgical Adjuvant Breast and Bowel Project randomized phase III trials (B-22, B-25, B-28, and B-30). Our cohort included 11 251 patients with no special type and 1231 with invasive lobular carcinoma. Patients with invasive lobular carcinoma were older, had larger and more frequently estrogen receptor-positive tumors, and more positive lymph nodes. During early follow-up (0-5 years), patients with invasive lobular carcinoma had fewer recurrences (hazard ratio [HR] = 0.797, 95% confidence interval [CI] = 0.685 to 0.929) and deaths (HR = 0.756, 95% CI = 0.623 to 0.917). After 5 years, patients with invasive lobular carcinoma had more recurrences (HR = 1.30, 95% CI = 1.085 to 1.558) and deaths (HR = 1.044, 95% CI = 0.898 to 1.214). Conditional probability analysis showed statistically significant interactions between time-period and histologic type for recurrences (P < .001) and deaths (P < .001). Patients with invasive lobular carcinoma have elevated risk of late recurrence and death compared with patients with no special type cancers.