Hi Bio_as,
If I understand your question, I think you are asking how cancer ends up in the left breast, right breast or both. I can only give you my opinion, but as a breast
cancer survivor I had
cancer in both breasts and I believe what cancer ended up in what breast was fate. I know I have a hereditary component (I'm positive for BRCA2), but as to where it occurs, I think it's fate or chance.