Differences in Prognostic Factors and Failure Patterns Between Invasive Micropapillary Carcinoma and Carcinoma With Micropapillary Component Versus Invasive Ductal Carcinoma of the Breast: Retrospective Multicenter Case-Control Study (KROG 13-06)

We performed a retrospective multicenter study comparing patients with carcinoma with micropapillary component (IMPC) and randomly matched patients with invasive ductal carcinoma (IDC) of similar age (+/- 3 years), pathologic T and N stage, treatment method, and date of surgery (within 1 year) performed at the same institution. Lymphovascular invasion and high nuclear grade were more frequent in IMPC compared to matched IDC. Locoregional recurrence-free survival and recurrence-free survival rates were different between these groups. Purpose: We designed the present study to investigate differences in prognostic factors and failure patterns between patients with invasive micropapillary carcinoma or carcinoma with micropapillary component (IMPC) and randomly matched patients with invasive ductal carcinoma (IDC) of the breast at multiple institutions of the Korean Radiation Oncology Group (KROG). Materials and Methods: This retrospective multicenter study was performed using subjects treated from January 1999 to November 2011. Female patients who had undergone curative resection for breast cancer without neoadjuvant chemotherapy were considered for this study. Exact matches were made for age (3 years), pathologic tumor and node stage, treatment method (surgery with or without radiotherapy), and period when surgery was performed (within 1 year) at the same institution. Results: A total of 534 patients were analyzed. The median follow-up period was 59 months in both groups. In the comparison of clinicopathologic characteristics, rates of lymphovascular invasion (LVI) and nuclear grade III were both significantly higher in IMPC than in IDC (P < .001, P = .01, respectively). During the follow-up period, recurrences developed in 40 patients with IMPC (15.0%) and 21 with IDC (7.9%). Locoregional recurrence (LRR) developed in 22 patients with IMPC (8.2%) and 10 with IDC (3.7%). The rate of distant metastasis did not differ between the 2 groups (P = .52). LRR-free survival (P = .03) and recurrence-free survival (P = .007) were significantly different between the 2 groups, but overall survival was not (P = .67). Conclusion: IMPC is associated with a higher rate of LVI, high nuclear grade, and a propensity for LRR compared to IDC. Modification of the locoregional treatment modality might be needed in this pathologic subtype of breast cancer.