The Absolute Effect / Evidence / COMICE
COMICE
In women with biopsy-proven breast cancer planned for wide local excision after conventional assessment, does routine preoperative breast MRI reduce reoperation?
Trial registry: ISRCTN57474502 · One underlying study; follow-up publications consolidated.
Design, population and eligibility
UK multicentre randomized controlled trial across 45 centres.
1,623 women randomized: 816 to preoperative MRI and 807 to no MRI.
Biopsy-proven breast cancer with planned wide local excision after clinical examination, mammography with or without ultrasound and pathology.
Primary surgical endpoint assessed after initial surgery and subsequent reoperation.
Treatment and comparator
Preoperative contrast-enhanced breast MRI added to conventional triple assessment; MRI findings could influence surgical planning.
Conventional clinical assessment and standard imaging without routine preoperative MRI.
Primary endpoint: Reoperation after breast-conserving surgery.
Other endpoints: Mastectomy, additional surgery and cost-effectiveness; no survival endpoint powered.
Key efficacy results
Reoperation occurred in 19% of each group; OR 0.96 (95% CI 0.75–1.24), P=0.77.
The trial did not demonstrate a reduction in reoperation from routine MRI. A subsequent evidence review reports mastectomy in 7% of the MRI group versus 1% without MRI, highlighting the possibility of more extensive surgery after MRI findings. MRI use also altered surgical decisions, so downstream mastectomy and biopsy pathways are important to interpret.
Source-reported outcome visualization
Reoperation after initial breast-conserving surgery · Primary surgical outcome
Rounded percentages as reported in the primary publication. No absolute benefit is demonstrated.
Absolute effect
Absolute difference in reoperation was approximately zero percentage points (19% versus 19%). No NNT is appropriate.
NNT: Not applicable; no demonstrated absolute reduction.
NNH: Not calculated; a reliable fixed-horizon harm endpoint is not supplied by the primary abstract.
Toxicity, harms and treatment burden
MRI can trigger additional imaging, biopsies, anxiety, delay and potentially more extensive surgery; these downstream consequences should be assessed individually.
The trial's primary report does not provide a unified grade 3–5 toxicity endpoint because MRI is a diagnostic strategy rather than an anticancer treatment.
MRI-related additional procedures and false-positive findings are the relevant burdens; do not equate these with treatment toxicity.
Quality of life and patient-reported outcomes
No robust quantitative QoL advantage was established in the primary trial report. Psychological burden, additional investigations and treatment delay should be acknowledged but not assigned invented rates.
Subgroups, maturity and limitations
COMICE was conducted in an earlier MRI and biopsy workflow era; image-guided biopsy access and multidisciplinary pathways have since evolved.
The result concerns routine MRI for all eligible women, not MRI for selected indications such as lobular histology, occult primary, extent uncertainty or neoadjuvant response assessment.
The study was not designed to demonstrate a survival difference.
Clinical interpretation
Current-practice context · 1 November 2026 (full guideline freshness review pending): Use MRI selectively when the result is likely to change management and when MRI-detected lesions can be appropriately sampled before changing surgery. Current guidance and local diagnostic pathways should determine indications.
Primary sources and registry
Source hierarchy: primary randomized report and prespecified follow-up first; registry and current guidance are supplementary. Values not reported in the cited primary sources are explicitly marked unavailable rather than imputed.