Wick, Michael J.

397 Background: Carcinomas of the appendix are exceedingly rare tumors and have an annual age-adjusted incidence of around 0.4 cases per 100,000. Appendiceal adenocarcinoma accounts for <0.5% of all gastrointestinal neoplasms and, of these, mucinous adenocarcinomas account for the majority. Published accounts of familial instances of primary appendiceal tumors are strikingly rare. Methods: We report two siblings who both developed primary mucinous adenocarcinomas. A genetics evaluation was conducted to determine if there was a recognizable underlying single gene disorder: no DNA mismatch repair defect was evident and no other diagnosis was apparent. A review of appendiceal cancers seen at Mayo Clinic from l997 to the present was conducted to search for additional familial cases. Results: Among 316 cases of primary appendiceal cancer of any histologic type, this sib pair was the only family reporting a second affected family member. Conclusions: The occurrence of appendiceal cancer in siblings may represent a random occurrence. Adenocarcinomas of the most common type of appendiceal cancer and occur at older ages than other histologic subtypes. A strikingly rare predisposition syndrome cannot be ruled out. [Table: see text] No significant financial relationships to disclose.