Most cases of primary hyperparathyroidism are due to benign tumors (adenomas) on one or more parathyroid glands. And in most of those cases, we don’t have a good explanation for why the tumor grows. We know that the risk for developing a parathyroid tumor is higher in women, and is higher in older people. And we know that there are genetic causes for parathyroid tumors, though most people with parathyroid tumors will not have one of those genetic mutations.

When a surgeon takes out a parathyroid tumor, he or she will remove the entire parathyroid gland. So you will not get another tumor on that gland (unless part of the gland was left behind). Some people will have tumors on more than one gland, which is why it is good to look at all four parathyroid glands during the operation. If there are multiple tumors, then you remove multiple glands (although you don’t want to remove all four - you need some parathyroid tissue to regulate calcium levels). If your surgeon leaves you with just normal glands, there is a theoretical risk that you could develop another tumor on one of the other glands down the road, but this is rare. Most people will need one operation, and will not develop more tumors later on.