A new prospective study has reported that the best breast cancer screening method and schedule for women at high risk of breast cancer because of a family history is an annual MRI. The authors compared clinical breast examination, mammography, ultrasound, and quality-assured breast magnetic resonance imaging (MRI), used alone or in various combinations. The study included 687 women seen in several centers who had no signs of breast cancer or symptoms, but who had an estimated lifetime risk of a least 20% due to familial breast cancer. For 371 of the women, additional half-yearly ultrasounds and breast examinations were performed.

The women were followed for an average of 29 months, during which time 27 were diagnosed with breast cancer. Eleven (41%) had ductal carcinoma in situ and 16 (59%) had invasive breast cancer. Three (11%) of the 27 were lymph node positive. All of the breast cancers were detected during annual screening. No interval cancer (cancer found by the women themselves between screening visits) occurred and no cancer was identified during half-yearly ultrasound.

Study participants underwent at total of 1,679 annual screening rounds. The cancer yield (cancer found) of ultrasound (6.0 of 1,000) and mammograms (5.4 of 1,000) was equivalent. The yield increased (7.7 of 1,000), but not significantly, when both methods were used in combination. However, the cancer yield of MRI alone (14.9 of 1,000) was significantly higher. Furthermore, the cancer yield of MRI was not significantly improved by adding mammography (MRI plus mammography: 16.0 of 1,000) and it did not change by adding ultrasound (MRI plus ultrasound: 14.9 of 1,000). The fraction of cancers found per 100 abnormal findings was 39% for mammography, 36% for ultrasound, and 48% for MRI. The authors conclude that in women at elevated familial cancer risk, MRI screening shifts the distribution of screen-detected breast cancers toward the preinvasive stage. Neither mammography, nor annual or half-yearly ultrasound or clinical breast examination is likely to add to the cancer yield achieved by MRI alone in high-risk women screened annually.

Some MRIs in place of mammograms would reduce cumulative radiation dose

The study results call into question current guidelines recommending mammography in addition to MRI for screening of high risk women. The authors conclude that mammography appears to be unnecessary in women undergoing MRI and suggest that the guidelines should be revisited. Using MRIs instead of mammograms would reduce the cumulative radiation dose associated with regular mammographic screening, which starts at a young age (25 to 30 years old) for high risk women. The study also provides evidence that problems that have been reported associated with MRIs, namely, a high rate of false positives and insufficient sensitivity for DCIS, can be avoided. This suggests that women should have their MRIs at a well-recognized breast cancer center with a high volume of breast MRIs (but not the sort of capacity constraints that would tend to prevent radiologists from delivering the highest possible quality readings).