Annual versus less frequent mammographic surveillance in people with breast cancer aged 50 years and older in the UK (Mammo-50): a multicentre, randomised, phase 3, non-inferiority trial

In 114 NHS hospitals, Mammo-50 evaluated whether less frequent mammographic surveillance is non-inferior to annual mammography in terms of breast cancer-specific survival (BCSS), in patients (age ≥50 years) who had undergone surgery for invasive breast cancer or DCIS and remained recurrence-free at three years.

The standard of care arm (n=2618) was annual mammograms for 9 years from surgery (6 years from trial entry). In the ‘less frequent mammogram’ arm (n=2617), mastectomy patients received mammograms at years 6 and 9; breast conserving surgery (BCS) patients received mammogram at years 5, 7 and 9 (with BCS and mastectomy patients having had annual mammograms up to year 3, prior to recruitment). 

With a median of 5.7 years follow up (IQR 5.0-6.0; 8.7 years post surgery), there was no difference in BCSS (annual mammogram 98.1%; ‘less frequent’ 98.3%). Overall survival at 5 years was 94.7% and 94.5% respectively.

The study was powered to 5000 and over recruited (n=5235). However compliance was 83% for annual mammography and only 69% for the ‘less frequent’ arm. BCSS was assessed in the intention-to-treat population. Although not powered to report in the ‘per protocol’ subgroup, no difference was seen (97.8% [n=2170] vs 98.0% [n=1817] respectively). The study primarily included lower risk-of-recurrence patients: small, low-grade and ER-positive tumours (82·7%), with 74% age ≥60 years. In the context of the  NHS (where  5 years annual mammogram is standard), Mammo-50 suggests that omitting year 4 mammogram after BCS, and omitting year 4 and 5 after mastectomy (if followed by a year 6 mammogram) is safe.

- Summary written by Lay In Lim, Specialist Surgical Registrar at Royal Oldham Hospital