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]