Peritoneal carcinomatosis of unknown primary site, a study of 25 patients over 30 years

Peritoneal carcinomatosis may be diagnosed by cytology or CT-guided biopsy, but routine radiologic and endoscopic workup not reveal a primary site. The clinical condition is referred to as peritoneal carcinomatosis of unknown primary site.

Over a 30-year time interval all patients treated with an initial diagnosis of carcinomatosis of unknown primary site were managed on a special clinical pathway. Upper gastrointestinal endoscopy, colonoscopy, and abdominal and pelvic CT were performed. Immunostains suggested a gastrointestinal origin of the carcinomatosis. After these tests, exploratory laparotomy was performed.

Twenty-five patients fulfilled the criteria for peritoneal carcinomatosis of unknown primary site and all 25 of these patients underwent an exploratory laparotomy. Special attention to the anatomic site of the appendix occurred during the exploratory laparotomy. No site within the gastrointestinal tract including a non-cancerous appendix was observed in 9 patients (36%). In 7 patients (28%), the carcinomatosis was so extensive that an adequate exploration to determine a primary site was not possible. In a third group of 9 patients (36%), exploratory laparotomy revealed an occult appendiceal malignancy.

Peritoneal carcinomatosis of unknown primary site was caused by an occult appendiceal adenocarcinoma in 36% of our patients. This error in diagnosis may lead to suboptimal treatment. Surgical exploration to visualize the anatomic site of the appendix should occur prior to making a definitive diagnosis of peritoneal carcinomatosis of unknown primary site.