Progesterone receptor status and tumor grade predict the 21-gene recurrence score of invasive lobular breast cancer

Aim: To assess the association between established clinicopathological variables and the 21-gene recurrence score (RS) stratification of invasive lobular carcinoma (ILC) of the breast. Materials & methods: We identified 9030 ILC patients from the Surveillance, Epidemiology and End Results database. Results: Older age, higher grade tumor and progesterone receptor (PR)-negative disease were independent predictors of high-risk RS stratification. Among patients with PR-positive tumors, 3, 6 and 15% with well-differentiated (G1), moderately-differentiated (G2) and poorly and/or undifferentiated (G3) disease were in the high-risk cohort, respectively. In patients with PR-negative tumors: 16, 24 and 41% of patients with G1, G2 and G3 disease were in the high-risk cohort, respectively. Conclusion: The 21-gene RS testing may not be necessary for patients with PR+/G1-2 ILC.