Prognostic significance of ductal carcinoma <i>in situ</i> coexisting with invasive ductal carcinoma: Biological behavior, immune response and survival outcomes

Biological differences exist between invasive ductal carcinoma (IDC) and IDC + ductal carcinoma <i>in situ</i> (DCIS) tumors including variations in tumor grade, hormone receptor status, human epidermal growth factor receptor 2 (HER2) expression, proliferative activity and molecular subtype. The present study evaluated the impact of the coexistence of IDC + DCIS on tumor microenvironment, tumor-infiltrating lymphocytes (TILs), clinical and pathological features, prognosis and survival. A total of 165 patients with IDC and 404 with IDC + DCIS were enrolled and treated in the outpatient clinic, Hacettepe University Department of Medical Oncology (Ankara, Turkey) between January 2014 and July 2021. Compared with IDC, patients with IDC + DCIS were more likely to be hormone receptor-positive and had a lower rate of mastectomy and Ki-67 index (both P<0.05). The co-existence of DCIS was associated with significantly improved overall survival (OS) and disease-free survival (DFS) (both P<0.05). Furthermore, patients with IDC had 2.14-fold higher odds of death and 2.44-fold higher odds of recurrence/distant metastasis/death than patients with IDC + DCIS. The present study supports the behavioral differences of IDC and IDC + DCIS and suggests these two groups of tumors may also behave differently in terms of antitumor immune response. As the DCIS component is positively associated with favorable prognostic features, the presence of the DCIS is associated with improved DFS and OS. DCIS accompaniment may have prognostic value for patients with breast cancer.