Parathyroid cancer is a rare cancer of the parathyroid glands. There are four parathyroid glands and they surround the thyroid gland in the front of the neck. The cancerous cells may cause an increase in the amount of parathyroid hormone (PTH) in the body. This results in increased calcium blood levels and related symptoms such as bone pain, kidney stones, weakness and confusion. The cancer usually occurs in individuals in their 50's and 60's.