1990年以来，我院遇到3例多原发性癌，术前均未能诊断该病，兹结合3例误诊教训，对多原发性癌的诊断、分类及易发部位讨论如下。临床资料例1，女，39岁。腹痛1个月，腹泻3周，伴脓血便半月，进行性消瘦。入院诊断为直肠癌伴不全梗阻，直肠镜检示肿块距肛缘11cm，术前病理未能确 Since 1990, 3 cases of multiple primary cancers have been encountered in our hospital. The disease was not diagnosed before surgery. We combined 3 cases of misdiagnosis. The diagnosis, classification, and site of susceptibility to multiple primary cancers are discussed below. Clinical data Example 1, female, 39 years old. Abdominal pain 1 month, diarrhea 3 weeks, with pus and blood for half months, progressive weight loss. The hospital diagnosis was rectal cancer with incomplete obstruction. The rectal microscopic examination revealed that the mass was 11cm away from the anal margin. The preoperative pathology was not confirmed.