Periductal myxoid stroma identifies ductal carcinoma in situ at risk of invasive recurrence.

Overtreatment of breast ductal carcinoma in situ (DCIS) remains a major clinical problem because clinicopathologic criteria are insufficient to define the invasive potential. We evaluated whether periductal stromal morphology in diagnostic hematoxylin-eosin sections predicts invasive recurrence among 711 DCIS patients from the randomized SweDCIS trial, who underwent breast-conserving surgery with or without radiotherapy. Two raters scored the proportion of DCIS ducts surrounded by myxoid stroma. Eighty patients developed ipsilateral invasive recurrence as first event post surgery. Cause-specific Cox regression revealed that an increase in myxoid stroma was associated with a higher risk of invasive recurrence (adjusted HR per 10% increase = 1.16 [1.04-1.28]; p = 0.005). The 20-year cumulative incidence of invasive recurrence was more than doubled for lesions with at least 10% myxoid stroma compared with those with less than 10% myxoid stroma (15.7% vs 7.1%). Periductal myxoid stroma may be a simple histologic marker for the invasive potential of DCIS.