Unmasked Testicular Seminoma During Use of Hormonal Transgender Woman Therapy: A Hidden hCG-Secreting Tumor.

Management of gender-affirming hormone therapy (HT) in transgender women includes surveillance of testosterone (T) levels. Failure of T to suppress, despite adherence to therapy, warrants additional investigations for unexpected sources of T or factors stimulating T secretion. Possible causes include T or gonadotropin production by an occult neoplasm. Testicular cancer is the most common malignancy affecting biological men aged between 15 and 35 years. Patients may be asymptomatic until tumor burden is high and/or metastatic. Hormone-producing tumors have rarely been reported in treated transgender women. Routine screening tests are recommended in a gender-incongruent person as per the 2017 Endocrine Society guidelines with measurement of T levels every 3 months initially to reach a goal of less than 50 ng/dL. Expectations should be discussed in detail with the transgender person since anticipated physical changes may not be notable for 6 to 18 months. We herein describe a case of a transgender woman who underwent standard HT including gonadotropin suppression with a gonadotropin-releasing hormone agonist, whose total T level failed to suppress. Testing revealed an elevated serum level of the beta subunit of human chorionic gonadotropin (β-hCG), diagnostic of an hCG-secreting testicular seminoma, as the underlying cause of unexpected T production. This case illustrates how easily a testicular cancer can remain unnoticed because it can be asymptomatic and the necessity to be alert to, and act on, anomalous laboratory results during treatment of a transgender person.