Sexual and gender minority (SGM) people, including agender, asexual, bisexual, gay, gender diverse, genderqueer, genderfluid, intersex, lesbian, nonbinary, pansexual, queer, and transgender people, comprise approximately 10% or more of the U.S. population. Thus, most oncologists see SGM patients whether they know it or not. SGM people experience stigma and structural discrimination that lead to cancer disparities. Because of the lack of systematic and comprehensive data collection, data regarding SGM cancer incidence, outcomes, and treatment responses are limited. Collection of data regarding sexual orientation, gender identity, transgender identity and/or experience, anatomy, and serum hormone concentrations in oncology settings would drastically increase collective knowledge about the impact of stigma and biologic markers on cancer outcomes. Increasing the safety of oncology settings for SGM people will require individual, institutional, and systems changes that will likely improve oncologic care for all patients.