Dear Alicia, I have also had experiences with friends of mine who
have had breast cancer and then were advised to not breastfeed.  I am
a lactational physiologist, and have done serious literature searches
to see if anyone has done a proper study to look at the ability to
breastfeed after breast cancer.  There is not a single experimental
or epidemiologic study published on this to my knowledge.

In regard to your specific question about steroids during lactation,
it is well known that lactation (on a population basis) serves as the
world's most important contraceptive.  A good review of this is an
article by Peter Howie called "Natural regulation of fertility."  It
is published in the British Medical Bulletin, vol. 49, pp. 182-199.
Clearly, ovulation (and hence estrogen) is much more likely to occur
sooner in women who choose to not breastfeed their infants.

In regard to the question concerning the protective effect of
breastfeeding on the risk of breast cancer... A most recent very
good study concerning this is of the epidemiologic nature.  It is by
Polly Newcomb et al., and is published in the New England Journal of
Medicine, vol. 330, pp. 81-7.  This is a retrospective, epidemiologic
study that found that the risk of premenopausal breast cancer is
reduced by approximately 22% when a woman has breastfed an infant.
Interestingly, this effect was the greatest when the woman breastfed
an infant before she was 20 yrs (risk was reduced by 50%).  Many
other epidemiologic studies have been done, and are sited in this
article.

Hope this helps.

Shelley McGuire, Ph.D.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Shelley McGuire
Animal and Vet. Science
University of Idaho
Moscow, ID 83844
(208) 885-6351
FAX: 208-885-6420

"Life itself is the proper binge."
                                   -Julia Child, chef
+++++++++++++++++++++++++++++++++++++++++++++++++++++