PURPOSE: The Prosigna-PAM50 risk of recurrence (ROR) score has documented clinical utility for the prediction of 10-year distant recurrence (DR). The present study investigated the value of Prosigna-PAM50 for predicting 10-year DR and overall survival after 5 years of endocrine treatment for postmenopausal patients with invasive lobular carcinoma.

PATIENTS AND METHODS: Using the Danish Breast Cancer Group database, we identified patients with a diagnosis from 2000 to 2003 of estrogen receptor-positive, human epidermal growth factor receptor 2-negative invasive ductal (n = 1570) or lobular (n = 341) cancer > 20 mm or 1 to 3 positive lymph nodes and applied multivariate Cox models.

RESULTS: The median follow-up for DR was 9.3 years and for overall survival 15.2 years. Of the 341 lobular and 1570 ductal cases, 140 (41%) and 349 (22%) were classified as low ROR, with a 10-year DR rate of 7.7% (95% confidence interval [CI], 3.7%-13.6%) and 3.5% (95% CI, 1.8%-6.2%), respectively. The 10-year DR rate for the intermediate ROR group for those with lobular cancer was 18% (95% CI, 10.1%-27.9%) compared with 9.7% (95% CI, 6.7%-13.4%) for those with ductal cancer. Luminal B tumors had a significantly worse outcome than luminal A tumors in both lobular (hazard ratio, 1.89; 95% CI, 1.03%-3.45%; P = .04) and ductal (hazard ratio, 3.18; 95% CI, 2.29%-4.43%; P < .0001) cancer.

CONCLUSION: Prosigna PAM-50 provides significant prognostic information beyond the clinicopathologic factors in patients with invasive lobular breast cancer. Those with lobular cancer had worse 10-year DR rates compared with those with ductal cancer in the same ROR category. Our results could have an effect on the treatment decisions regarding the addition of chemotherapy for those in the intermediate ROR group.