Metastasis of non-muscle-invasive bladder cancer into the thyroid gland: a literature review accompanied by a rare case.

Bladder cancer is the most prevalent malignancy of the urinary tract. About 90% of bladder cancers are urothelial carcinomas. Seventy percent of cases newly diagnosed are superficial diseases; roughly 30% of newly diagnosed cases are muscle-invasive metastatic diseases. Bladder urothelial carcinoma primarily metastasizes into regional lymph nodes and then into liver, lung, mediastinum, bone, and adrenal gland. In our case, non-muscle-invasive bladder cancer metastasized into the bone, mediastinum, iliac lymph node, and adrenal and thyroid glands. This is the first reported case in the current literature in which urothelial carcinoma metastasized into the thyroid gland.