Breast conservation and negative margins: how much is enough?

There is no standard definition of what constitutes an adequate negative margin of resection in invasive cancer or ductal carcinoma in situ (DCIS). The definition of a negative margin used in randomized trials was tumor not touching ink. Tumor touching ink, whether invasive or DCIS, increases the risk of local recurrence (LR). In invasive cancer, convincing evidence that more widely negative margins decrease the risk of LR is lacking, and multiple other biologic and treatment factors influence the risk of LR. In DCIS treated with radiotherapy, evidence that margins wider than 2mm are beneficial is also lacking. Techniques of pathologic processing are a source of variation in margin assessment. The need for margins larger than tumor not touching ink (invasive cancer) and 2mm (DCIS) should be considered in the context of the multiple other factors known to impact upon LR.