William Stewart Halsted was a surgeon at Johns Hopkins Hospital in Baltimore, Maryland, during the late 1800s and early 1900s. In 1894 Halsted described his procedure for treating breast cancer by removing the breast tissue, chest muscles, and lymph nodes in the armpit, a procedure he named radical mastectomy, and that became the standard of care for treating breast cancer until 1970. He also made contributions to other novel medical procedures such as gallbladder surgery, blood transfusions, antiseptic techniques, anesthesia use, and using plates and screws to hold bones in position when setting bone fractures. At Johns Hopkins Hospital, Halsted established a surgical training program in which he allowed medical students and surgical residents to shadow him and perform procedures under his guidance. In the twentieth century, similar training programs spread across the country and informed the standardization of medical training. Halsted devised a surgical treatment for breast cancer and reshaped the way physicians practiced medicine in the twentieth century, which resulted in better health outcomes through more careful surgical methods, especially in women with breast cancer.

Gender-affirming mastectomy is a type of surgery that removes breast tissue, tightens the skin, and can adjust nipple placement to provide the desired results of a more masculine-looking chest. Mastectomies started as a way for surgeons to remove breast cancer and tumors from the breast tissue. However, as of 2022, surgeons also use the procedure as a means of gender-affirming surgery for transgender and non-binary, hereafter TNB, individuals. If a person identifies as transgender, their gender identity differs from the sex they were assigned at birth and the gender they were most likely raised as, which can produce gender dysphoria, a condition that can last a lifetime. Non-binary individuals may have a similar experience, but they identify outside of or between the identifiers of man and woman. Gender-affirming mastectomy, sometimes called top surgery, improves the quality of life for people who seek the appearance of a masculine chest to both better integrate themselves into society and lessen the mental and emotional burden of gender dysphoria.

In 1894, William Stewart Halsted published The Results of Operations for the Cure of Cancer of the Breast Performed at the Johns Hopkins Hospital from June, 1889, to January, 1894, in the medical journal Annals of Surgery. In the article, Halsted describes the results from fifty of his operations on women with breast cancer, performed at Johns Hopkins Hospital in Baltimore, Maryland. Those operations involved a surgical procedure Halsted called radical mastectomy, which consists in removing all of the patient’s breast tissue, chest muscle, and underarm lymph nodes. Halsted’s surgery effectively cured breast cancer in a time period when no other effective treatment options were available. The radical mastectomy remained the standard of care from the 1890s to the 1970s as a means of treating a type of reproductive cancer common to women.