The worst case scenario they used was if someone at risk for breast cancer got mammograms early. The horror, but also the cost savings from early detection! If you claim your grandmother had breast cancer you will no hassle getting a mammogram at an early age, there should be no difference if you have genetic hints at the same risk-factor. No insurer would pay for a preventative mastectomy without strong medical evidence (e.g. not just a genetic test), there's no sense in bringing up a world-famous rich actress who almost assuredly paid for her surgery out of pocket.

The most expensive thing for a health insurer is the customer who doesn't get a mammogram when she should.