RT Journal Article SR Electronic T1 De-differentiation of papillary thyroid carcinoma into squamous cell carcinoma. A case of coexistence within an excised neck lesion JF BMJ Case Reports FD BMJ Publishing Group Ltd SP bcr2012007707 DO 10.1136/bcr-2012-007707 VO 2012 A1 William David George Evans YR 2012 UL http://casereports.bmj.com/content/2012/bcr-2012-007707.abstract AB An 80-year-old man with papillary thyroid carcinoma of the neck underwent surgery and radioiodide therapy. He presented 11 years later with a lesion adjudged from fine needle aspiration to be a squamous cell carcinoma (SCC). Histological analysis of the excised mass revealed a lymph node overwhelmed with papillary thyroid carcinoma and moderately differentiated SCC thought to have transformed from papillary cells. A very small number of similar transformations specifically involving the ‘tall cell variant’  of papillary carcinoma transforming to spindle cell carcinoma have been reported previously. This case report demonstrates clear images of this rare occurrence and briefly considers factors leading to de-differentiation. The clinician should consider possible transformation from papillary thyroid cancer in cases of SCC of the head and neck as this variation may be more aggressive.