I was once at the Shabbos table when the hostess quipped that every woman she knows who developed breast cancer had an unhappy marriage. While I acknowledged that there is definitely an emotional component to developing cancer in any form, I don't know if I would go so far to say that an unhappy marriage was the sole reason for developing the disease. Given that Ashkenazi women are particularly prone to that type of cancer, it would be a disservice to label all those women as unhappily married.
Now a study was just released that demonstrates that undergoing even a couple years of stress increases a woman's risk of developing breast cancer by sixty-two percent! That's an incredible amount if you ask me, not to mention pretty shocking when you consider how many women undergo extended periods of "unhappiness" in their lives.
You can read the article here.