Changes in patient management after preoperative MRI for newly diagnosed breast cancer: a multicentre prospective observational study.

Objectives: To understand whether and how breast magnetic resonance imaging (MRI) at cancer diagnosis influences treatment planning, and whether subpopulations of patients with newly diagnosed breast cancer benefit in terms of most appropriate management.

Design: Multicentre prospective observational study.

Setting: Seven centres across New South Wales, Victoria and Western Australia during the period 15 September 2020 to 14 July 2022.

Participants: Patients with newly diagnosed early breast cancer meeting predefined criteria for whom multidisciplinary team normal practice deemed MRI would aid treatment planning.

Intervention: Preoperative contrast-enhanced MRI.

Main outcome measures: Reasons for requesting MRI; pre-MRI versus post-MRI changes in treatment plans; changes justified by pathology findings.

Results: 387 eligible participants were enrolled. MRI was most frequently requested for dense breasts (252 [65%]), clinical and/or radiological size discrepancy (161 [42%]), multifocality (108 [28%]) and young age (105 [27%]). Change in treatment plan after MRI occurred for 198 participants (51% [95% CI, 46-56%]), including a change in breast surgery plan for 119 participants (31% [95% CI, 26-36%]). More mastectomies were planned after MRI (15% v 28%; absolute risk difference [RD], 13 percentage points [95% CI, 9-17]; P < 0.001), including unilateral mastectomy (14% v 24%; RD, 10 percentage points [95% CI, 6-14]; P < 0.001) and bilateral mastectomy (1% v 4%; RD, 3 percentage points [95% CI, 1-5]; P < 0.001). No increases in planned mastectomies occurred for women aged ≥ 70 years (RD, -3 percentage points [95% CI, -15 to 9]; or in those for whom neoadjuvant therapy was planned (RD, 2 percentage points [95% CI, -11 to 14]). Change in surgery was deemed justified by pathology findings in 75 of 88 women who experienced a change (85% [95% CI, 75-91%]).

Conclusions: Preoperative MRI findings led to changes in surgical management for a third of selected women with early breast cancer, increasing the mastectomy rate. In most cases, the changes were deemed appropriate. MRI findings did not change planned mastectomy in those aged ≥ 70 years, indicating that these women may not experience changes in surgical plans after such testing.