Does pre-operative breast MRI have an impact on surgical outcomes in high-grade DCIS?

OBJECTIVES: High-grade DCIS (HG DCIS) is associated with upgrade to invasive disease but few studies evaluate the role of MRI in this subset of DCIS. This study compared surgical outcomes of females with HG DCIS on biopsy who had pre-operative MRI with those that proceeded directly to surgery. METHODS: This single-centre retrospective, observational study identified patients with pure HG DCIS on pre-operative biopsy from the pathology database. Surgical outcomes, clinicopathological and radiological features were obtained for all patients. RESULTS: From August 2015 to February 2020, 217 patients had HG DCIS on biopsy. Pre-operative MRI was performed in 40 (MRI group) and not in 88 (No MRI group) patients. Initial mastectomy was performed in 25/40 (63%) women in the MRI group and 20/88 (23%) women in the no MRI group (p < 0.0001). No difference was observed in re-operation rate between the two groups, 15% in MRI group vs 22% in No MRI group (p = 0.4749). Mean tumour size on histology was larger in mastectomy cases in the MRI group (73.4 mm, range 6–140 mm), than the total MRI group, (58.3 mm, range 0–140 mm) or no MRI group (30.7 mm, range 0–130 mm) (p < 0.0001). CONCLUSIONS: Pre-operative MRI in HG DCIS is associated with higher mastectomy rates, possibly due to patient selection for MRI, as tumours on final histology were significantly larger. Fewer re-operations were observed in the MRI group although this was not significant. ADVANCES IN KNOWLEDGE: Breast MRI performed pre-operatively in HG DCIS is associated with higher mastectomy rates and fewer re-operation rates.