THERAPEUTIC AND DIAGNOSTIC FACTORS AS RELATED TO CANCER RISK

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Continuing with a long-standing interest in the relationship of iatrogenic agents to cancer risk, studies examined effects of oral contraceptives, menopausal hormones, and infertility drugs. In an international collaboration, oral contraceptives were shown to increase breast cancer risk only for recent users, with the effect dissipating after five or more years. Further analyses within a case-control study to elaborate on reasons for the high risk associated with oral contraceptives for breast cancers diagnosed prior to 35 years of age showed that further attention should focus on potential interactions with race, family history, and alcoholic beverage consumption. In a follow-up study of breast cancer screening participants, neither oral contraceptives nor menopausal hormones appeared to affect the risk of subsequent colorectal cancers. Follow-up of a large cohort of Swedish women prescribed menopausal hormones showed a significant increased risk of endometrial cancer following estrogen use; women prescribed combination therapy were not at altered endometrial cancer risk, but did experience approximately a 40% elevated risk of breast cancer after 10 years of follow-up. In contrast, reduced risks of colorectal and liver cancers were observed. Mortality from all causes in relation to hormone use was also examined in this study. Also of concern is whether ovulation-stimulating drugs might increase the risk of certain cancers, particularly ovarian cancer. To address these concerns, a retrospective cohort study of 10,000 infertile women has been initiated. Cancer risk in relation to medical devices has also been of interest. Use of intra-uterine devices, particularly inert ones, appeared to reduce the risk of endometrial cancer. Although breast implants have been shown to interfere with mammographic visualization of breast lesions, a case-control study found them associated with reduced breast cancer risk, consistent with several earlier prospective studies. A large retrospective cohort study of 13,000 women with cosmetic implants is currently underway to ascertain whether different implants predispose to various forms of cancer as well as connective tissues disorders; of interest with respect to cancer risk is whether silicone implants predispose to multiple myeloma, as suggested by recent NCI laboratory findings.