New insights from MIPA study about magnetic resonance imaging before breast cancer surgery

The European Society of Radiology (ESR) recently published this press release:

The Multicenter International Prospective Analysis (MIPA) study provides novel insights into whether and to what extent breast magnetic resonance imaging (MRI) before surgery impacts surgical treatment in breast cancer practice and brings to light new evidence to inform the discussion on the use of breast MRI before surgery.

Breast MRI has been demonstrated to outperform mammography and ultrasonography in providing information on tumour extent and uncovering additional cancers undetected by conventional methods. Therefore, the routine use of breast MRI is argued to allow more tailored surgical planning. However, over the last two decades, preoperative breast MRI has been considered to prompt a very large increase in mastectomy, thereby counteracting the trend in favour of breast conserving surgery. This highlights the need for a better understanding of the effect of preoperative breast MRI on clinical decision-making.

Under the lead of Prof. Francesco Sardanelli, Professor at the University of Milan and Director of Radiology Department at the IRCCS Policlinico San Donato, the research team behind the MIPA study (study protocol published in 2020) conducted a large-scale evaluation of the clinical practice of performing or not performing breast MRI in thousands of patients newly diagnosed with breast cancer. Data from 5,896 patients (excluding candidates to neoadjuvant therapy) were collected from 27 qualified clinical centres worldwide between June 2013 and November 2018 and subsequently analysed. The paper reporting the main results of the MIPA study has been just published in European Radiology (https://doi.org/10.1007/s00330-021-08240-x).

The first interesting data is that 692 of 5896 patients had breast MRI for screening or diagnostic purposes, i.e. the cancer was diagnosed with breast MRI: for more than one in five women breast MRI was used for surgical planning even though it was not performed with “preoperative” intent, a setting that could be named as “preoperative breast MRI by default”. These cases were excluded by the primary results and a specific analysis on this subgroup is ongoing.

Comparing 2441 patients who had preoperative breast MRI (MRI group) with 2763 patients who did not (noMRI group), the main findings were the following. Surgeons participated in requesting MRI in about 45% of the cases, showing the real routine practice where surgeons frequently ask for this examination. Patients sent to MRI were younger and more in pre/perimenopausal status, had denser breasts, a higher proportion of multifocal/multicentric cancers diagnosed before MRI on conventional imaging (mammography/ultrasound), a higher proportion of cases of invasive lobular histopathology, and a tumor size at final pathology equal to or larger than 20 mm (T2 or higher stage), all differences being highly significant. This data shows a specific selection for preoperative breast MRI of women with a higher risk of mastectomy. Of note, the proportion of women with mastectomy already planned before MRI was higher in the MRI group (22.4%) than in the noMRI group (14.4%), again with high significance, so that in many cases MRI was used as a “confirmation tool” for a mastectomy already planned before MRI.

The rate of mastectomy after MRI was 33.7%, with 2.0% due to the woman’s choice, 0.5% due to other reasons, and 8.8% as additional mastectomy rate associated with MRI. These data are compared with 15.6%, 0.7%, and 0.5% in the noMRI group, respectively. Only in 0.3% of cases, we observed a conversion from mastectomy to conserving surgery by MRI. The reoperation rate for positive margins was significantly lower (8.5%) in the MRI group than in the noMRI group (11.7%). The overall mastectomy rate (also including mastectomies as a second intervention) was 36.3% versus 18.0%, respectively. Regarding women of the MRI group who underwent conserving surgery, MRI did not alter the surgical extent in 84.5% of cases. The remaining 15.5% received less extensive surgery (1.6%), more extensive single excision (11.3%), or multiple excisions (2.6%), this 15.5% representing 10.4% of the entire MRI group.

The MIPA results clearly show that the discussion on the routine use of breast MRI before surgery needs to take into account that: 1) for over 20% of the cases, we have a “breast MRI by default” (the cancer is diagnosed with MRI); 2) surgeons ask for preoperative MRI in 45% of the cases; 3) usually patients with a higher mastectomy risk are referred for preoperative MRI (in about two thirds of mastectomies, this surgical treatment is already the option of choice before MRI, so MRI is used as a “confirmation tool”); 4) with this selection, an additional mastectomy rate of 9% is observed, counterbalanced by a reduction in reoperation rate by about 3%; 5) women of the MRI group who received conserving surgery had a more tailored excision in 16% of the cases (10% of the entire MRI group).

The MIPA study provides new insights on the controversial topic of preoperative breast MRI. MIPA results can support discussion in tumour boards when preoperative MRI is under consideration and should be shared with patients to achieve informed decision-making.

Acknowledgements
The MIPA study was managed by the European Institute for Biomedical Imaging Research (EIBIR) under the scientific lead of Prof. Francesco Sardanelli, University of Milan and IRCCS Policlinico San Donato. MIPA was promoted by the European Network for the Assessment of Imaging in Medicine (EuroAIM), an EIBIR joint initiative, and endorsed by the European Society of Breast Imaging (EUSOBI). The study received an unconditional research grant from Bayer AG.

Reference
Sardanelli, F., Trimboli, R.M., Houssami, N. et al. Magnetic resonance imaging before breast cancer surgery: results of an observational multicenter international prospective analysis (MIPA). Eur Radiol (2021). https://doi.org/10.1007/s00330-021-08240-x

Press contact
Katharina Krischak
kkrischak@eibir.org
+43 1 533 40 64 13