<prompt> Serum calcitonin may be elevated inIslet cell tumour of pancreasChoriocarcinoma of ovaryCarcinoid tumour of appendixMedullary carcinoma of thyroid  <response>: Calcitonin is a polypeptide of 32 amino acids derived from ultimobranchial body. It is secreted from C cells of thyroid parafollicular cells. It lowers the plasma calcium and phosphorus levels. It blocks the PTH induced bone resorption. Calcium from the circulation is shunted into the bone. It increases the excretion of calcium, phosphorus, sodium and potassium. Normally it is less than 0.08 ngL undetectable. It is increased in medullary carcinoma of thyroid. It is very good tumour marker for MCT. It confirms the relapse metastasesresidual disease. Increased levels in family members confirm the genetic relation and such relatives should undergo prophylactic total thyroidectomy. Reference : page 488 SRBs manual of surgery 5th edition 