<prompt> Answer this question truthfullyWhat is the staging classification for Medullary thyroid cancer?  <response>: <reason> According to the American Joint Committee on Cancer AJCC there are 4 stages of medullary thyroid cancer based on the clinical features and findings on imaging. Each stage is assigned a letter and a number that designate the tumor size, number of involved lymph node regions, and metastasis.Primary tumor Tumor size Sub-stage Finding Image T0 No evidence of primary tumor T1 Tumor 2 cm in greatest dimension limited to the thyroid T1 a Tumor 1 cm, limited to the thyroid T1 b Tumor 1 cm but 2 cm in greatest dimension, limited to the thyroid T2 Tumor 2 cm but 4 cm in greatest dimension, limited to the thyroid T3 Tumor 4 cm limited to the thyroid, or gross extrathyroidal extension invading only strap muscles T3 a Tumor 4 cm limited to the thyroid T3 b Gross extrathyroidal extension invading only strap muscles sternohyoid, sternothyroid, thyrohyoid, or omohyoid muscles from a tumor of any size T4 Tumor includes gross extrathyroidal extension beyond the strap muscles T4 a Tumor with gross extrathyroidal extension invading subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve from a tumor of any size T4 b Tumor with gross extrathyroidal extension invading prevertebral fascia or encasing the carotid artery or mediastinal vessels from a tumor of any size. TX Primary tumor cannot be assessed Regional lymph node involvement Node involvement Sub-stage Finding Image N0 No lymph node involvement N0 a One or more cytologically or histologically confirmed benign lymph nodes N0 b No radiologic or clinical evidence of locoregional lymph node metastasis N1 Metastasis to regional nodes N1 a Metastasis to level VI or VII pretracheal, paratracheal, or prelaryngeal Delphian, or upper mediastinal lymph nodes. This can be unilateral or bilateral disease N1 b Metastasis to unilateral, bilateral, or contralateral cervical neck lymph nodes levels I, II, III, IV, or V or retropharyngeal lymph nodes NX Regional lymph node cannot be assessed Distant metastasis Presence of metastasis Sub-stage Finding Image M0 No distant metastasis M1 IV Distant metastasis 