Tumor grade and progesterone receptor status predict 21-gene recurrence score in early stage invasive breast carcinoma

Purpose: The 21-gene recurrence score (RS) assay is increasingly utilized to predict the risk of recurrence in early stage estrogen receptor (ER)-positive breast cancer. We hypothesize that tumor grade and progesterone receptor (PR) status predict RS categorization. Methods: We identified women between the ages of 18 and 74 years with stage I or II, ER-positive, invasive carcinoma of the breast from the Surveillance Epidemiology End-Results database from 2010 to 2013. Multivariable logistic regression was performed to determine factors associated with high-risk RS. Results: We identified 42,530 patients that met inclusion criteria. Multivariable logistic regression demonstrated that grade I tumors [OR (odds ratio) 0.33, 95% CI (confidence interval) 0.31–0.37] and PR positive (PR+) status (OR 0.16, 95% CI 0.15–0.17) were significantly less likely to be associated with high-risk RS. Of patients with grade I PR+ tumors, 1% was in the high-risk group by the traditional cutoffs and 4% was in the high-risk group by the TAILORx cutoffs. The percentage of patients with high-risk RS remained low for grade I PR+ tumors regardless of age, race, tumor size, and lymph node status. Conclusions: We found that grade I PR+ tumors are associated a < 5% probability of having high-risk RS regardless of other patient demographic or pathologic factors. This suggests that the histologic factors of grade and PR status should be taken into consideration before ordering the 21-gene recurrence score assay.