Second primary cancers in patients with gastrointestinal cancers.

The occurrence of multiple primary malignant neoplasms in 9,191 consecutive cases of primary gastrointestinal (GI) tract cancer from 1962 to 1981 at the National Cancer Center was analyzed. The person-years of the cases totaled 28,399.4: 185 second cancers were diagnosed clinically and 85 were first diagnosed at autopsy. The overall frequency was 2.01% for clinically recognizable cancers and 2.94% including those discovered at autopsy. The overall observed/expected ratio was 0.96 for clinical cancers and 1.33 including autopsy cases. However, a significant association between the first and second cancers was present in the oro-pharynx and esophagus; esophagus, stomach and colon; stomach and all other parts of the GI tract; and the colon and rectum. The mode of appearance was also analyzed to clarify the organ relationship.