<prompt> Which of the following Ca thyroid have worst prognosisFollicular carcinomaPapillary carcinomaAnaplastic carcinomaMedullary carcinoma  <response>: Anaplastic carcinoma of thyroid has the worst prognosis. All anaplastic carcinomaa are stage 4. T4a is intrathyroidal anaplastic carcinoma which is surgically resectable. While T4b is extrathyroidal anaplastic carcinoma which is surgically unresectable. Lifespan is counted in few weeks to months only. 5 year survival is less than 15. Reference: SRBs Manual of Surgery, 6th Edition, page no 475. 