The concept of hormone-dependent cancers, or cancers that are sustained by particular hormones, developed slowly during the period from about 1940–1990. I chart how the development of the notion of hormone-dependent cancers initially relied upon assumptions that cast androgens and estrogens, prostate cancer and breast cancer, as opposite ends of a gendered hormonal binary. Starting in the 1940s, cancer researchers began to argue that “male sex hormones” (androgens) exacerbated prostate cancer and that “female sex hormones” (estrogens) ameliorated it. Within about a decade, cancer researchers suggested that the opposite might be true for breast cancer. By the 1980s, estrogens had come to dominate discussions of breast cancer's progression, diagnosis, and treatment. While historians of breast cancer and estrogen have discussed concerns surrounding estrogen exposures (debates about the safety of oral hormonal contraceptive pills, for example), they have not examined in detail the processes by which estrogen became closely linked to breast cancer. My research suggests that as breast cancer was redefined in terms of estrogen, scientific understandings of the function of estrogen shifted as well: breast cancer researchers began to emphasize the growth-promoting ability of estrogen as a central aspect of its hormonal function. This prioritization of the growth functions of estrogen complicated the gendered assumptions upon which the notion of hormone-dependent cancers initially relied. Researchers and clinicians began to suggest that estrogen could exacerbate some breast cancers not because it should be understood primarily as a “female sex hormone,” but because it could promote tumor growth.
