[Prostate cancer metastasized to thyroid cartilage: a case report]

A 75-year-old male was diagnosed as prostate cancer (serum PSA: 4,772 ng/ml, Gleason score: 4 + 4 = 8) with multiple bone metastases. And he noticed a painless mass of the frontal neck a month before the diagnosis. Computed tomography of the neck showed a tumor in the thyroid cartilage. Biopsy of the neck tumor revealed metastasis of prostate cancer by positive PSA staining. Metastasis of malignant tumor to cartilaginous tissue is extremely rare because there are usually no vessels in it. Only 4 cases of the metastasis of prostate cancer to the thyroid cartilage have been reported. It was thought that tiny bone marrows were formed in the ossified cartilage and it caused hematogenous metastasis.