There have been a few studies that look into the correlation between breast cancer and divorce rates. Some point to a correlation, while others do not support the hypothesis.
I have personally seen divorces happen during and following breast cancer treatment. Patients will cry and say their breast cancer caused their husband to leave them. They may believe that their spouse departed due to disfigurement, altered physical image (ie, weight gain, mastectomy, baldness), or emotional neediness that the spouse did not want to deal with.