<prompt> Medullary ca of thyroid is associated with increase in-CalcitoninThyroglobulinT3T4  <response>: Medullary carcinomas of thyroid are neuroendocrine tumours derived from the parafollicular cells or C cells. They secrete calcitonin,the measurement of which plays an impoant role in the diagnosis and post operative follow - up of patients.Calcitonin is readily demonstrable within the cytoplasm of tumour cells as well as in stromal amyloid by immunohistochemical methods. Ref: Robbins and cotrans 9e Pg 1099 