Ectopic Parathyroid Hormone Expression in Nonmetastatic Prostate Cancer

Ectopic expression of PTH in nonmetastatic prostate cancer is a rare occurrence. We present a case of a 60-year-old Chinese man who initially presented with hyperparathyroidism, PTH 80.1 pg/mL (SI: 8.5 pmol/L) (reference range, 8.5-58.5 pg/mL [SI: 0.9-6.2 pmol/L]), hypophosphatemia, 1.95 mg/dL (SI: 0.63 mmol/L) (reference range, 2.91-4.64 mg/dL [SI: 0.94-1.5 mmol/L]) and normal calcium levels, 2.27 mmol/L (SI 9.08 mg/dL) (reference range, 2.1-2.6 mmol/L [SI: 8.4-10.4 mg/dL]). Two years later, he was diagnosed with prostate adenocarcinoma. A whole-body bone scan ruled out osteoblastic metastases. Notably, the patient exhibited elevated urinary calcium excretion, 304.6 mg/day (SI: 7.6 mmol/day) (reference range, 33.2-272.6 mg/day [SI: 0.82-6.74 mmol/day]) and indeterminate urinary fractional calcium excretion (1.79%). A Technetium-99 sestamibi scan did not identify any hyperfunctioning parathyroid adenoma. Following treatment for prostate cancer, both hyperparathyroidism and hypophosphatemia resolved. Immunostaining of prostate cancer tissue revealed ectopic PTH expression. This case highlights a rare cause of hyperparathyroidism due to ectopic PTH secretion in prostate cancer, adding to known etiologies such as osteoblastic metastases, vitamin D deficiency, oncogenic osteomalacia, renal insufficiency, and primary hyperparathyroidism. Recognizing ectopic PTH expression is crucial for managing prostate cancer patients presenting with hyperparathyroidism.