Long term prognosis of ductal carcinoma in situ with microinvasion: a retrospective cohort study

Ductal carcinoma in situ with microinvasion (DCIS-Mi) is an early-stage breast cancer with long-term behavior, prognosis and treatment not fully understood. The aim of our study was to explore the clinicopathological and prognostic features of DCIS-Mi with pure DCIS and IDC-T1 (invasive ductal carcinoma with a tumor size ≤2 cm) as control. We retrospectively reviewed 242 cases of DCIS-Mi, 280 cases of pure DCIS, and 347 cases of IDC-T1. The clinicopathological features, therapeutic schemes and survival status were compared among the three groups. After a median follow-up of 109 months, the 5-year disease-free survival (DFS) was lower for the DCIS-Mi patients than for the DCIS patients but higher than the IDC-T1 patients (100%, 96.89% and 87.86% respectively, P<0.001). The 5-year breast cancer specific survival for DCIS-Mi patients was also between that of DCIS and IDC-T1 patients (100%, 99.32%, and 95.42% respectively, P=0.001). Tumor size (P<0.001, HR=18.31, 95% confidence interval (CI) 5.53-60.65) was identified as an independent prognostic factor for recurrence or metastasis. Furthermore, our study indicated that DCIS-Mi patients derived minimal, if any, benefit from chemotherapy treatment after mastectomy (P=0.63, HR=1.50, 95% CI 0.29-7.87). To our knowledge, this is the largest follow-up cohort study on Chinese DCIS-Mi patients. Our data suggested that DCIS-Mi exhibited worse clinical outcome than pure DCIS but better than that of IDC-T1. Tumor size was an independent prognostic factor. Post-mastectomy chemotherapy did not help for increasing DFS for DCIS-Mi patients.