Tumor-to-tumor metastasis: Hepatocellular carcinoma metastatic to parathyroid adenoma.

Tumor-to-tumor metastasis is a rare, but well-recognized phenomenon. Here, we report a unique case of hepatocellular carcinoma (HCC) metastatic to parathyroid adenoma. A 53-year-old-man with a history of HCC presented with hypercalcemia. It was found that he also had hyperparathyroidism with a hypoechoic mass in the lower portion of the right thyroid gland area. The patient underwent parathyroidectomy, and a mass measuring 1.5 × 1.0 cm was detected. Microscopic and immunohistochemical examination disclosed parathyroid adenoma with a focus of metastatic HCC. For the patient, it was the only distant metastasis revealed until the last follow-up. To the best of our knowledge, this is the first reported case of tumor-to-tumor metastasis in which HCC is the donor.