I met 2 sisters during my radiation treatment. Sister 1 had a mammogram and was diagnosed. Sister 2 wasn't due for a mammogram for another year but read somewhere that as her sister had breast cancer she should have yearly mammograms instead of every 2 years. So she had a mammogram too and an almost identical tumour was found. Her surgery was a week later than Sister 1 but their chemo and rads treatment was together.
I actually thought they were twins as they did look very similar but they were a few years apart. The younger sister was diagnosed first.