Method and results: A standardized histopathological protocol has been designed, in which different histological characteristics of ductal carcinoma in situ (DCIS) are reported: nuclear grade (ng), growth pattern according to Andersen et al., necrosis, size of the lesion, resection margins and focality. Using this protocol a re-evaluation of a population-based consecutive series of 306 cases of DCIS has been done as well as a thorough clinical follow-up. After a median follow-up of 63 months, 13% have developed ipsilateral local recurrences, invasive and/or in situ. Ipsilateral local recurrence-free survival (IL-RFS) was significantly better for patients operated with mastectomy (ME) or breast conserving therapy (BCT) with radiotherapy (RT) than for patients operated with BCT without RT (5-year IL-RFS 96% vs 94% vs 79%, P<0.001). In the subgroup of BCT without RT there were significant differences in IL-RFS between histopathological subgroups: ng 1 + 2 (non-high grade) vs ng 3 (high grade; P=0.014), non-high-grade without comedo-type necrosis vs non-high-grade with comedo-type necrosis vs high-grade (the Van Nuys classification system; P=0.025). Growth pattern (not diffuse vs diffuse) and margins (free vs involved or not evaluated) showed a tendency (P=0.07 and 0.05, respectively) to be associated to IL-RFS. In contrast, no significant differences in IL-RFS were found in subgroups based on mode of detection, focality or size. Ninety-four per cent of the local recurrences after BCT appeared at the previous operation site.
Conclusions: In the BCT without RT group, combinations of either non-high grade and not a diffuse growth pattern or non-high grade and free margins identified groups (constituting approximately 30% of the patients) were at low risk of developing ipsilateral recurrences (6-10%), compared to a 31-37% recurrence risk in the remaining groups during the observed follow-up time. The beneficial effect of post-operative RT for these low-risk groups can be questioned, and should be studied further.