A78-year-oldwomanhadasurgicalhistoryforcervicalcancerandoccultbreastcarcinoma.Theintraoperativefindingsduringlaparoscopiccholecystectomyatanotherhospitalshowedmultipleperitoneal nodulesandascitesinthediaphragm.Histologicalfindingsofaperitonealnoduleshowedserousadenocarcinoma.Becausethepostoperativeexaminationshowedsigmoidcoloncancerandbreastcancer,shewas referred to our hospital for treatment. Simultaneous triple cancer, including primary peritoneal cancer, sigmoid colon cancer, and breast cancer was diagnosed. Paclitaxel + carboplatin therapy was given for primaryperitonealcancer.AbdominalCTafter2coursesofchemotherapyshowedreducedascitesand peritonealnodularlesions,andsigmoidectomy,omentectomy,andovariectomywereperformed.Theprimaryperitonealcancerrelapsed,andthepatientdiedoftheoriginaldisease27monthsafterdiagnosis.