A 21 year-old Japanese female was referred to the hospital for evaluation of a mass in her neck. Cytologic samples obtained through fine needle aspiration (FNA) material from the mass showed pseudopapillary or sheet-like clusters. The cells had oval nuclei and columnar cytoplasms. Nuclear groove and intranuclear inclusions were scarcely seen. The cells had a cribriform or solid pattern, unlike cells in papillary thyroid carcinoma. This distinct cytological appearance is thought to belong to FAP (familial adenomatous polyposis)-associated thyroid cancer. The patient was diagnosed with FAP associated papillary thyroid carcinoma. FAP was confirmed by colonoscopy. Her mother, 48 years old, also detected an anterior neck swelling at the time of her daughter's admission. At the age of ten, the mother had undergone total colectomy because of FAP. FNA of the mass demonstrated the same cytological appearance as from her daughter's tumor. Total thyroidectomy was performed. Gross and microscopic appearances of the tumor was similar in mother and daughter. We believe it is possible to detect FAP through FNA cytology of thyroid tumors if pathologists are aware of the unique cytohistological features of thyroid tumor cells in FAP.
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