Micropapillary ductal carcinoma in situ of the breast: an inter-institutional study.

The clinical significance of micropapillary growth pattern in ductal carcinoma in situ is controversial and the impact of nuclear grading in terms of recurrence of this lesion is yet to be clarified. Our aim was to evaluate, on a series of micropapillary in situ carcinomas, the histological features correlated with recurrence and whether the micropapillary subtype had a different behavior from other non-micropapillary ductal carcinoma in situ. We collected 55 cases of micropapillary in situ carcinomas from four institutions. All cases were reviewed for nuclear grade, extent, necrosis, microinvasion and tested for estrogen and progesterone receptors, Ki67, HER2, EGFR and p53 expression. Clinical data, type of surgery and follow up were obtained for all patients. Our results showed that the nuclear grade is crucial in determining the biology of micropapillary carcinoma in situ, so that the high nuclear grade micropapillary ductal carcinoma in situ more frequently overexpressed HER2, showed higher proliferation index, displayed necrosis and microinvasion and was more extensive than low/intermediate nuclear grade. Logistic regression analysis confirmed the high nuclear grade (Odds ratio: 6.86; CI: 1.40-33.57) as the only parameter associated with elevated risk of local recurrence after breast-conserving surgery. However, the recurrence rate of 19 micropapillary carcinoma in situ, which were part of a cohort of 338 consecutive ductal carcinoma in situ, was significantly higher (log-rank test, P-value=0.019) than that of non-micropapillary, independently of the nuclear grade. In conclusion, although nuclear grade may significantly influence the biological behavior of micropapillary ductal carcinoma in situ, micropapillary growth pattern per se represents a risk factor for local recurrence after breast-conserving surgery.