Impact of the 21-gene recurrence score on outcome in patients with invasive lobular carcinoma of the breast

Invasive lobular carcinoma (ILC) of the breast has unique clinicopathologic characteristics, compared to invasive ductal carcinoma. The role of the 21-gene Recurrence Score (RS) has not been clearly defined for ILC. We sought to determine the prognostic value of RS and the impact of adjuvant chemotherapy on long-term survival in patients with ILC. Utilizing the Surveillance, Epidemiology and End Results database from 2004 to 2013, we identified records of women aged 18-74 years, diagnosed with estrogen receptor (ER)-positive ILC (stage I to III) with RS available. We categorized patients into risk groups based on the traditional RS cutoffs and into those of the Trial Assigning Individualized Options for Treatment (TAILORx). Five-year breast cancer-specific survival (BCSS) was analyzed using the Kaplan-Meier method and Cox proportional hazards models. Of the 7316 women included, 21% were in the low-risk; 71%, intermediate-risk; and 8%, high-risk groups as per TAILORx RS cutoffs. The 5-year BCSS was 99% in the low-risk, 99% in the intermediate-risk, and 96% in the high-risk groups. A high-risk RS as per TAILORx cutoff was independently associated with increased mortality (hazard ratio [HR] of death 2.37, 95% confidence interval [CI] 1.14-4.95) when compared to a low-risk RS. In both the high-risk and intermediate-risk groups, adjuvant chemotherapy was not significantly associated with the HR of death (high-risk, HR 1.14, 95% CI 0.55-2.38; intermediate-risk, HR 1.08, 95% CI 0.62-1.87). For patients with ER-positive ILC, 8% were in the high-risk and 72% were in the intermediate-risk groups as per the TAILORx RS cutoffs. In the high-risk group, the RS predicted a lower 5-year BCSS. Adjuvant chemotherapy did not seem to confer a survival benefit for either the intermediate- or the high-risk cohorts.