Primary hyperparathyroidism is almost always caused by one or more benign parathyroid tumors. These parathyroid tumors are almost never cancerous: parathyroid cancer is so rare that it is not discussed on this app at all. Questions about parathyroid cancer can be answered at http://www.parathyroid.com/parathyroid-cancer.htm
Patients who have primary hyperparathyroidism for a number of years tend to have a higher incidence of developing cancer within other organs. Several studies have shown that patients who have high blood calcium have nearly a two-fold increase in the development of breast, colon, kidney, and prostate cancer. These studies suggest that it is the duration of elevated calcium (how long the calcium has been high) which correlates to higher rates of cancer in these other organs. The development of these other cancers has nothing to do with how high the blood calcium has become, instead it is how long it has been high that is important. Even very small elevations of blood calcium for more than 5 years appears to increase the rate of developing cancer in these other parts of the body. This is why “observing” and “watching” the high calcium waiting for it to possibly get higher is not be the best management option. The complications of hyperparathyroidism (stones, osteoporosis, heart attack, stroke, A-Fib, and even the development of other cancers) are related to how many years the calcium has been high. Importantly, several of these same studies have found that removing the parathyroid tumor and curing the high calcium reverses the increased cancer risk.
It is not completely known why people with hyperparathyroidism have a higher chance of getting these other cancers, but there are several theories. One theory revolves around the calcium molecule itself which may turn on promoter genes for certain cancers, and turn off genes that inhibit the formation of cancer. Other theories center on vitamin D and the fact that the vast majority of patients with hyperparathyroidism have low vitamin D. The low vitamin D is protecting the patient from developing very high blood calcium levels, but it may be causing other problems. Clearly the answer is to remove the parathyroid tumor so these patients can be put on vitamin D. Remember, if your calcium is high, vitamin D should usually not be taken as it can make your blood calcium go very high. The ideal situation is to have the parathyroid tumor removed and then after the tumor is removed, the patient should be supplemented with vitamin D and calcium together to restore bone health and vitamin D levels.
For more information on this topic: http://www.parathyroid.com/parathyroid-symptoms.htm