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.