Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor. The identification of calcitonin as a specific and sensitive marker in 1968 determined a special interest of endocrinologists. Many hormones have been isolated in MTC tumors. Calcitonin, prostaglandins and somatostatin are of particular interest. Calcitonin is not only a marker, but is indicative of tumor size and prognosis. Moreover the presence of calcitonin receptors in MTC could have a role in the proliferation of this tumor. Somatostatin and the large use of somatostatin analogs in the treatment of neuroendocrine tumors raise the hope that these drugs could be effective in MTC patients. Unfortunately, the benefits of these treatments is not validated. More interestingly, nonsteroidal anti-inflammatory drugs could be of interest in this tumor by comparison of their use in colorectal polyps. By inhibiting Cox or inducing 15 PGDH enzymes, we have demonstrated in vitro its effectiveness. Thus, hormones in MTC are not only markers but probably mediate biological effects involved in tumor growth.