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Abstract Background: Estrogen exposure is a known risk factor for the development of breast cancer in women. Less clear is the risk posed by gender affirming hormone therapy (GAHT) in both transgender men and transgender women. We aimed to characterize the breast cancers that have arisen in our institution’s transgender patient population including biomarker profile, method of diagnosis, and stage at diagnosis. Methods: For this retrospective cohort study, patients from the Mount Sinai Health System were identified using the electronic medical record from 2016-2023. A cohort of transgender or non-binary patients with breast cancer was established by using ICD-10 codes for carcinoma in situ of breast (D-05) and malignant neoplasm of breast (C-50) and a diagnosis or medical history encompassing gender identity disorders (ICD-10-CM: F64) or a chief complaint related to transgender health. Chart review enabled selection of patients who have a history of GAHT. Patients with incomplete medical records were excluded from analysis. Results: 14 patients met criteria and were included for final analysis. Mean age at diagnosis was 51.7 (31-65) years and 86% (12/14) were at or above 40 years of age at diagnosis and eligible for routine screening mammography. The cohort encompassed six trans men (assigned female at birth), seven trans women (assigned male at birth), and one genderqueer person (assigned female at birth). Family history was not significant for most of the cohort. Two patients had a first-degree relative with a history of breast cancer; both were BRCA negative. Four patients (29%) were diagnosed via screening mammography; six patients (43%) were diagnosed after palpating a breast or axillary mass; and four patients (29%) had not undergone screening but were diagnosed via breast imaging mandated prior to planned chest masculinization surgery. At time of initial presentation, the diagnostic stage was DCIS in five patients (36%); LCIS in one patient (7%); stage 1 cancer in four patients (29%); stage 2 cancer in three patients (21%); and breast implant-associated anaplastic large cell lymphoma in one patient (7%). 50% (7/14) of patients had an active or past prescription for testosterone-based GAHT, and 50% (7/14) patients had an active or past prescription for estrogen-based GAHT. Mean duration of all GAHT prior to diagnosis was 16.6 years (mean duration of estrogen-based GAHT was 27.6 years and mean duration for testosterone-based GAHT was 5.7 years). Biomarker profiles were available for twelve patients; 8/12 (67%) patients were diagnosed with estrogen receptor (ER) positive cancer, four (33%) with ER negative cancers. Of patients on estrogen-based GAHT, three presented with ER+ and four presented with ER- cancers. 10/14 patients had bilateral mastectomies and 4/14 had lumpectomies. Discussion/Conclusion: The mode of cancer detection suggests that screening mammography is under-utilized among transgender and non-binary patients who use GAHT. This represents a health care disparity involving a vulnerable patient population. The biomarker profile among this population demonstrates that both estrogen-responsive and estrogen-nonresponsive cancers can arise in the setting of prior or ongoing gender affirming estrogen or testosterone. Citation Format: Nithya Krishnamurthy, Ethan Ravetch, Christina Weltz. Breast cancer among transgender and non-binary patients on gender affirming hormone therapy: a single institution experience abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-10-02.
Krishnamurthy et al. (Thu,) studied this question.