title: Carcinoma in situ in a lateral cervical cyst.
abstract: BACKGROUND
  The development of an invasive squamous cell carcinoma within a lateral cervical cyst as a result of malignant transformation of the epithelium is considered a rare circumstance. The existence of this entity is a source of controversy in light of the differential diagnosis, which includes a cervical metastasis from an unknown primary carcinoma (CUP-syndrome). Apart from site, histologic findings, and follow-up, the principal diagnostic criterion for lateral cervical cyst carcinoma is the histomorphologic demonstration of transition of the benign epithelium into invasive squamous cell carcinoma. Although numerous case reports of this entity exist, carcinoma in situ in a lateral cervical cyst has been reported in only five cases thus far.
  
  
  METHODS
  In this context, we present the case of a 44-year-old patient with a 7-month history of cervical swelling.
  
  
  RESULTS
  After diagnostic extirpation of the tumor, histologic findings were consistent with a lateral branchial cyst with high-grade dysplasia and carcinoma in situ of the squamous epithelial lining.
  
  
  CONCLUSIONS
  This case of a premalignant lesion within a lateral branchial cyst (ie, carcinoma in situ) supplies the "missing link" and adds credibility to the concept of primary branchiogenic carcinoma.
mesh_terms: D000328:Adult; D001935:Branchioma / Q000473:pathology; D002278:Carcinoma in Situ / Q000473:pathology*; D003560:Cysts / Q000473:pathology*; D006258:Head and Neck Neoplasms / Q000473:pathology*; D006801:Humans; D008297:Male