I am sorry to hear about your friend, itself.

A few years ago, there was quite a bit of discussion on prophylactic mastectomy, i.e. prevention measures against breast cancer. At that time, what I gathered (but I wasn't paying extreme attention) was that the benefits of such preemptive measures were not all that obvious, and that it was still possible to get breast cancer despite having had one's breasts removed.

Now, the treatment might have evolved in the meantime, I don't know.

In any case, I would never get genetic testing myself, for any disease that I can think of.

But, seeing it from a distance, I also see the gene testing like an industry, a fear-driven industry, so I am naturally suspicious...