European guidelines on breast cancer screening and diagnosis

Should tailored screening with magnetic resonance imaging, in addition to mammography (either digital breast tomosynthesis or digital mammography) vs. mammography alone be used in organised population based screening programmes for early detection of breast cancer in asymptomatic women with high mammographic breast density? 

The GDG agreed that the balance of desirable and undesirable effects favours not implementing additional MRI for screening women with high mammographic breast density with negative mammography (either DBT or DM), but the evidence is uncertain. The overall certainty in the evidence is very low because of the uncertainty in the estimates for breast cancer mortality, breast cancer incidence, interval breast cancers, and false positive recall rate. The evidence informing these conclusions is from studies of women with high mammographic breast density detected by DM, but the evidence also applies to women screened with DBT (and the effects may be smaller when DBT is used).

The evidence shows that there may be large benefits with the addition of MRI. There may be more breast cancers detected in the first round of screening (1.6 more per 100), of which 1.3 are invasive. The evidence is very uncertain for a reduction in breast cancer deaths (1 fewer per 100 women with high breast mammographic density), the number of breast cancers detected in the second round (0.6 more per 100), and whether cancers detected between screening (interval cancers) is reduced (0.4 fewer per 100). In addition, overdiagnosis may be reduced when adding MRI (0.4 per 100). However, there may be large harms: adding MRI may increase the number of women incorrectly called back for another exam due to false positive findings (9 more per 100), but this evidence is very uncertain. Overall, the large desirable effects of adding MRI may be equivalent to the undesirable effects.

There would be large costs associated with MRI, but the overall cost-effectiveness of adding MRI could vary across settings. The GDG agreed that most women would probably find additional MRI acceptable, but it is probably not acceptable to health care systems given limited human resource capacity, and the necessary specialised training. It is also probably not feasible to implement due to the increased number of MRIs that would be necessary, the reduced accessibility to MRI in many countries, the lack of quality assurance, and the scarcity of gadolinium. While the addition of MRI to current screening protocols (including frequency) is likely not feasible, it could be feasible in future with other screening protocols, or with screening intervals that could potentially be longer than current intervals. Given the lack of accessibility and feasibility, the GDG agreed that adding MRI would increase health inequities.

The studies included mostly women with BI-RADS D. Given that there may be fewer benefits in women with BI-RADS C, the recommendation to not implement additional MRI might be considered even stronger in this group.

The acceptability of not providing an MRI may vary amongst women. Therefore, when asked, it will be important to share information about classification of breast density, availability of MRI, and the benefits and harms of MRI for women with high mammographic breast density and a negative mammography. 

Research priorities include:

• more research into measuring and classifying breast density,
• information to provide to women and communication,
• studies evaluating different screening frequencies and age to stop screening in women with high mammographic breast density,  and the use of abbreviated MRI.
• the role of Artificial Intelligence should be further investigated,
• the creation of an European consortium for a screening database would be beneficial in evaluating the efficacy of additional tests (e.g. MRI, ABUS, abMRI).