That's a good question. I don't follow the issue of lesbianism as much as I do male homosexuality. Now you have me curious.
There have been a few studies that seem to indicate that since lesbians as a group are less likely to have children, they are more likely to contract breast cancer than the general population of Heteros that do give birth. This may also account for the rise in breast cancer among all women since many put off pregnancy till they're in their mid-late 30's.