I-131 is mentioned in the Jan. 1994 Pediatrics issue (Vol 93 no. 1, pp137-150) entitled "The transfer of drugs and other chemicals into human milk." They state that radioactivity is present in milk up to 14 days. As far as the question about increased risk of breast cancer in the lactating breast, I'm sure there are no studies to substantiate such a claim (if anyone has such data, I would be fascinated!). After all, how many studies have retrospectively asked women whether they had I-131 during lactation, or prospectively studied women with I-131 exposure to see if they developed breast cancer? So, it would seem pure speculation by someone who appears to be looking for reasons for mom to wean. As someone who looks for reasons for moms to continue breastfeeding whenever possible, I could as easily speculate that the increased blood flow during lactation would facilitate clearing of the radioisotope as long as the milk is being regularly expressed, thereby decreasing the risk of breast cancer. Unless this doctor can provide research-based evidence that lactation increases this mother's risk in this setting, I vote for "pump and dump" for a minimum of two weeks, then continued breastfeeding. Alicia. [log in to unmask]