Apalutamide-Induced Hypothyroidism Associated With Increased Thyroid Hormone Clearance in Metastatic Prostate Cancer...

Apalutamide (APA) is an androgen receptor signaling inhibitor widely used for metastatic hormone-sensitive prostate cancer (mHSPC), though it can induce hypothyroidism. We report a severe case of APA-induced hypothyroidism in a patient with a history of total thyroidectomy.

A 65-year-old man receiving levothyroxine (175 μg/day) after thyroidectomy was diagnosed with mHSPC (Gleason score 4 + 4; PSA 13 904 ng/mL) with findings suggestive of cancer-associated disseminated intravascular coagulation. Following APA initiation (240 mg/day), PSA decreased rapidly to 0.01 ng/mL. However, TSH levels rose progressively despite increasing levothyroxine to 275 μg/day. After a 4-month follow-up interruption, TSH reached 187.9 mIU/L. APA withdrawal led to rapid TSH improvement.

Careful TSH monitoring is essential during APA treatment, especially in patients with pre-existing thyroid dysfunction or prior thyroidectomy. Appropriate levothyroxine titration and multidisciplinary collaboration are essential for the continuation of oncological therapy with APA.