Comprehensive analysis of the 21-gene recurrence score in invasive ductal breast carcinoma with or without ductal carcinoma in situ component

BACKGROUND: Invasive ductal carcinoma (IDC) is often accompanied by ductal carcinoma in situ (DCIS). Whether the DCIS component affects the 21-gene recurrence score (RS) is unclear. METHODS: Consecutive ER-positive, HER2-negative, N0–1 patients with RS results were included. Patients were divided into pure IDC and IDC with DCIS (IDC/DCIS) groups. The RS, the expression of its 16 cancer genes and prognosis were compared between IDC and IDC/DCIS patients. RESULTS: A total of 1458 patients were enrolled, 320 of whom had concomitant DCIS. DCIS component was independently associated with lower RS (P = 0.038). IDC/DCIS patients more often had a low-risk RS (P = 0.018) or intermediate-risk RS (P = 0.024). Regarding individual genes in the RS panel, Ki67, CCNB1 and MYBL2 in the proliferation group and MMP11 and CTSL2 in the invasion group were significantly lower among IDC/DCIS patients than pure IDC patients. Among IDC/DCIS patients, lower RS was independently correlated with a higher DCIS proportion and lower DCIS grade. Within a median follow-up of 31 months, the DCIS component in IDC did not significantly influence prognosis. CONCLUSIONS: IDC with DCIS component is associated with a lower 21-gene RS, possibly due to lower expression of proliferation and invasion genes. DCIS proportion and grade independently influenced the 21-gene RS in IDC/DCIS patients. Due to the relatively short follow-up period and low recurrence rate, the impact of the DCIS component in IDC on prognosis needs further evaluation.