Overall survival is improved when DCIS accompanies invasive breast cancer.

Invasive ductal carcinoma (IDC) often presents alone or with a co-existing ductal carcinoma in situ component (IDC + DCIS). Studies have suggested that pure IDC may exhibit different biological behavior than IDC + DCIS, but whether this translates to a difference in outcomes is unclear. Here, utilizing the National Cancer Database we identified 494,801 stage I-III breast cancer patients diagnosed with either IDC alone or IDC + DCIS. We found that IDC + DCIS was associated with significantly better overall survival (OS) compared to IDC alone (5-year OS, 89.3% vs. 85.5%, p < 0.001), and this finding persisted on multivariable Cox modeling adjusting for demographic, clinical, and treatment-related variables. The significantly superior OS observed for IDC + DCIS was limited to patients with invasive tumor size < 4 cm or with node negative disease. A greater improvement in OS was observed for tumors containing ≥25% DCIS component. We also found IDC + DCIS to be associated with lower T/N stage, low/intermediate grade, ER/PR positivity, and receipt of mastectomy. Thus, the presence of a DCIS component in patients with IDC is associated with favorable clinical characteristics and independently predicts improved OS. IDC + DCIS could be a useful prognostic factor for patients with breast cancer, particularly if treatment de-escalation is being considered for small or node negative tumors.