Does Medicare-eligible high-risk breast cancer screening MRI target the right women?

Introduction: MRI is the most sensitive modality to screen for breast cancer, but it is expensive with somewhat limited access. Audit of screening performance should reflect appropriate population targeting. Methods: An observational study on consecutively screened high-risk women, assessment of the contralateral breast staging a new cancer, or surveillance in women with prior breast cancer or high-risk lesion in Perth, Western Australia. All breast MRI studies from 1 January 2015 to 7 September 2018 were included. Studies were 3T comprising T2, DWI, ADC and T1-weighted +/- fat saturation +/- IV gadolinium, +/- subtraction. DCE was read on the dynamics or DynaCAD (Invivo, Gainesville, FL, USA). Fellowship-trained breast radiologists blindly double-read by consensus; additional reader/s arbitrated. The reference standard was the histopathology result or cancer registry notification for cancer diagnoses and benign biopsies, benign follow-up imaging or subsequent screening MRI. Results: Of 993 MRI studies in 554 women, 870 eligible MRI were performed in 471 women, and 706 had a reference standard. Median age was 44 years (range 18–80). The majority of studies (65% 457/706) were screening Medicare rebate-eligible high familial risk; 26% for surveillance after a breast cancer or contralateral staging; 6% screened BRCA carriers. Eleven cancers were diagnosed, eight were MRI-detected. Only two of these were at high-risk screening MRI. Five were detected at staging contralateral ILC, after negative 2D mammography and ultrasound. Cancer prevalence was highest for staging contralateral ILC, at 600/10,000 MRI, for high-risk screening 77/10,000 MRI and surveillance 116/10,000 MRI. Conclusions: Cancers were predominantly detected in women undergoing preoperative staging of new invasive lobular carcinoma in the contralateral breast, rather than the Medicare rebate-eligible high-risk screening group.