Patients were evaluated who had a history of at least two primary primary breast cancers (bilateral or asynchronous ipsilateral), with the first diagnosis made before the age of 65. Of these, 4 were homozygous for this variant, 75 were heterozygous, and 393 did not have it. In the controls there were 7 homozygous, 250 heterozygous, and 2203 not carrying the variant.
Testing this with the PGP calculator and assuming a lifetime risk of breast cancer of 12%, the PGP calculator estimates that carriers have an attributable increased risk of ~6% (total risk of ~18%).
These authors report finding no association between this variant and the risk of breast or ovarian cancer. Notably this study was much larger than Johnson et al., with a 39-year prospective study of 5,743 women, and a case-control with 1,201 cases and 4,120 controls.