Progestins are probably useful adjuncts to estrogen in preventing postmenopausal osteoporosis. Lindsay et al1 showed that the progestin gestronol hexanoate (not available in the United States) prevents bone loss from the metacarpals, and the efficacy of other progestins is currently being evaluated by measuring the mineral content of vertibral spongiosa by computed tomography, as described by Genant et al.2 Of the progestins available in the United States, hydroxyprogesterone caproate and the compounds mentioned by Dr Nadjafi seem to be effective (Gilbert S. Gordon, MD, oral communication, 1983). The safety of these compounds in the treatment of patients who have had breast cancer, however, has not been established. After all, estrogens are also used to treat breast cancer, so Dr Nadjafi's argument for their use is tenuous. I would agree, however, that the risk is small and acceptable if the patient is adequately informed.
Hoffman PG. Progestin Prophylaxis of Osteoporosis-Reply. JAMA. 1983;249(13):1710. doi:10.1001/jama.1983.03330370024021