Papillary carcinoma arising in ectopic thyroid tissue within a branchial cyst.

The first case of a papillary carcinoma arising in ectopic thyroid tissue within a branchial cyst in a 34 yr old woman is presented. This also adds to the existing list of unusual sites where ectopic thyroid tissue has been described. All histological types of carcinoma have been reported in ectopic thyroid tissue, papillary carcinoma being the most common histological type, accounting for 85% of these tumors. The criteria for establishing this diagnosis of carcinoma arising in ectopic thyroid tissue within branchial cyst is discussed.