A 35-year-old man comes to the office due to a progressive increase in breast size over the past 6 months. He is sexually active, has no chronic medical conditions, and takes no medications. The patient does not use tobacco, alcohol, or illicit drugs. Vital signs are normal. BMI is 28 kg/m². Gynecomastia with mild bilateral breast tenderness is present. Genitourinary examination reveals a 1-cm nodule in the right testis. The examination is otherwise normal. Laboratory results are as follows: Which of the following is the most likely diagnosis in this patient?

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11ec25c8_d92c_51d2_bc81_4d78a4380ea5_MD0003_00 This patient with a testicular mass, gynecomastia, and elevated estrogen levels likely has a Leydig cell tumor, the most common type of testicular sex cord stromal tumor. These tumors arise from supporting cells of the testes such as Leydig, Sertoli, and granulosa cells; they account for approximately 5% of testicular tumors (germ cell tumors account for ~95%), arise in a wide range of ages, and have no clearly defined risk factors. Leydig cells are the primary source of testicular testosterone but are also capable of generating estrogen. Therefore, Leydig cell tumors often present with endocrine manifestations due to excessive estrogen (eg, gynecomastia, loss of libido, erectile dysfunction) or testosterone (eg, acne, hirsutism). Examination frequently reveals a testicular mass, which is typically confirmed by bilateral scrotal ultrasound. In contrast to many germ cell tumors, Leydig cells do not generally produce serum tumor markers such as β-hCG or alpha-fetoprotein (AFP). However, the generation of estrogen or testosterone often leads to FSH and LH suppression. suppression (Choices A, D, and E) Choriocarcinoma, teratoma, and yolk sac tumors are nonseminomatous germ cell tumors. They typically present with a painless, firm testicular mass. However, they often produce β-hCG (particularly choriocarcinoma) or AFP (particularly yolk sac tumors); in addition, estrogen production is rare, so feminization is uncommon. (Choice C) Seminoma is a germ cell tumor that does not usually produce β-hCG, AFP, or estrogen. Therefore, feminization would be atypical. Most seminomas present with a painless, unilateral testicular mass or swelling. Educational objective: Leydig cell testicular tumors often cause feminization (eg, gynecomastia) due to the production of estrogen by tumor cells. This frequently causes secondary inhibition of FSH and LH. Serum tumor markers (eg, β-hCG, AFP) are not usually elevated.

A 35-Year-Old Man Comes to the Office Due to a Progressive