The aim of our study is to investigate patient selection for the 21-gene recurrence score assay (RS) for breast cancer (BC) and the RS impact on chemotherapy administration (Chemo) in clinical practice across the United States through the retrospective observational study of National Cancer Data Base (NCDB) patients from 2010 to 2012. NCDB captures ~70 % of all newly diagnosed malignancies in the USA annually. The 2010-2012 period depicts data from the beginning of the NCDB that required recording of molecular assays and their data release in April 2015. De-identified demographic and clinical variables of patients that had RS results were analyzed. 513,080 patients had BC; 406,525 were estrogen receptor-positive (ER+). 74,334/91,651 patients with RS recorded as a numerical value (0-100) were analyzed (18.2 % of ER+). Patients' ages ranged from 18 to 90 (mean = 58.8, median = 59); 99.1 % were females. Patients of Caucasian race, from regions with <7 % having no high school education, and >$63,000 median household income were more likely to be tested than patients of other races, education, or income (p < 0.001). 58.1 % of tests were performed in ER+/lymph node-negative/>1 cm tumors; 16.4 % included ≥N1 disease; 9.9 % included T1a, T3, Stage III and IV, or HER2-positive cancers. Low-risk RS result had 92.2 % negative predictive value for no Chemo. Intermediate-risk RS result had 40.1 % positive predictive value (PPV); high-risk RS had 81.2 % PPV for Chemo. RS is obtained in ~1/5 of ER + BC patients across the USA. Further studies investigating influence and implementation of the newest evidence-based management guidelines regarding patients' selection for RS test and chemotherapy administration upon obtaining of test results are warranted.
Keywords: 21-gene recurrence score assay; Breast cancer; Clinical practice; Oncotype DX.