In Medullary carcinoma of the thyroid or medullary thyroid cancer, the cancer is caused by abnormal division and proliferation of specific thyroid cells that produce the hormone calcitonin. Calcitonin is a small protein that undergoes abnormal aggregation in this disease and precipitates in the thyroid as amyloid. However, the amyloid is not considered dangerous and the main illness in this disease is the cancer itself.