Serum calcitonin may falsely estimate tumor burden in chronic hypercalcemia: a case of prostatic and multiple bone metastases from medullary thyroid cancer.

BACKGROUND

Medullary thyroid cancer (MTC) is a calcitonin (Ct)-secreting tumor of the parafollicular or C cells of the thyroid gland. Higher serum Ct levels are associated with larger tumor size, distant metastases, and prognosis. We report herein a case of prostate and multiple bone metastases of nonfamilial MTC with mildly elevated Ct levels.

METHODS

A 73-year-old man who was found to have a 2.5 cm MTC in the left thyroid lobe with cervical lymph node metastases presented with confused mental status because of severe hypercalcemia (albumin-modified serum calcium concentration 15.2 mg/dL) associated with multiple bone metastases. Prostate biopsy was performed because the patient had frequent urination with mildly elevated serum prostate-specific antigen (5.297 ng/mL). Histologically, the prostate was diagnosed as MTC metastasis, forming a tissue architecture closely resembling the previously diagnosed MTC, and the cells were positive for Ct, carcinoembryonic antigen, and thyroid transcription factor 1. Although the patient had multiple MTC metastases, basal and calcium-stimulated serum Ct levels were not significantly elevated, measuring 22.7 pg/mL (normal <10 pg/mL) and 22.1 pg/mL, respectively.

CONCLUSIONS

A chronic hypercalcemic state may exhaust Ct reserves and diminish the Ct response to an acute intravenous calcium injection. Therefore, the Ct level of a patient in a hypercalcemic state should be carefully interpreted. To our knowledge, this is the first reported case in the literature in which serum Ct levels were not significantly increased when associated with hypercalcemia, and an MTC metastasis to the prostate.