There is a study linking patients with previous thyroid cancer as being more prone to developing some form of breast cancers later. Breast cancer is also linked to colon: women with breast have been found to have 3% chance of also developing colon cancer - hence screening for both are very important. Of course there are tons of on-going studies.
My mother and her mom both had thyroid cancer early in life and my mom developed breast cancer at 46. The specialists at MD Anderson have informed her they are starting to relate radiation use for thyroid cancers to cause certain breast cancers.