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.