Background: Breast ductal carcinoma in situ with microinvasion (DCIS-Mi) is considered to be the interim stage in the progression from DCIS to invasive breast cancer (IDC). Cases that exceed DCIS-Mi but still do not fulfill the diagnostic criteria of IDC often are observed. We define those cases as DCIS with invasion component (DCIS-I), and attempt to study the differences of clinicopathological features and immunohistochemical-based subtypes among DCIS, DCIS-Mi, and DCIS-I.
Methods: In this retrospective study, 550 consecutive DCIS patients were recruited, 271 (49.3%) cases were diagnosed as pure-DCIS, 67 as DCIS-Mi, and 212 as DCIS-I. They were categorized into four groups: luminal-A (ER+ and/or PR+, HER2-), luminal-B (ER+ and/or PR+, HER2+), ERBB2+ (ER-, PR-, HER2+), and basal-like (ER-, PR-, HER2-).
Results: DCIS-Mi and DCIS-I patients tended to have larger tumors with highly graded nuclear (P = 0.011 for size; P < 0.0001 for nuclear grade). The proportion of luminal-like tumors decreased, whereas ERBB2+ and basal-like tumors increased in DCIS-I/DCIS-Mi compared with pure-DCIS (P = 0.039). Although the HER2-positive tumors displayed a stable proportion among DCIS subgroups, the essences of them were varying. In pure-DCIS, luminal-B was the major subtype of HER2-positive tumors (luminal-B vs. ERBB2+, 19% vs. 14.6%), whereas in DCIS-I, the proportion of luminal-B decreased vastly (luminal-B vs. ERBB2+, 12.8% vs. 23.5%). DCIS-I had a worse relapse-free survival outcome compared with pure-DCIS.
Conclusions: Different distribution of subtypes and distinctive characteristics among DCIS, DCIS-Mi, and DCIS-I indicate that they are distinct entities. Further studies with larger sample size are needed to replicate our observations.