Incidence of Multiple Primary Cancers. II. Index Cancers Arising in the Stomach and Lower Digestive System

Abstract

A cohort study of multiple primary cancers was conducted on patients treated during 1949–62, at the Memorial Sloan-Kettering Cancer Center, for cancers arising in the stomach and lower digestive system. Comparison with the New York State incidence rates revealed no increase in the number of associated or subsequent cancers of other organs or tissues among the index patients with cancer of the stomach or of the digestive organs proximal to the colon and rectum. Among the 4,771 patients with cancer of the colon and rectum, the proportion with previously (1.9%) and synchronously (3.6%) associated multiple primary cancers of the large intestine was 5.5%. The incidence of metachronous multiple primary cancers of the large intestine was 3.5 per year per 1,000 patients at risk, which represented an overall threefold excess in the observed number of primary cancers of the colon and rectum. In the patients with their index cancer in the cecum, the highest ratios were recorded of observed-to-expected cancers in both the large intestine (6.3) and other organs or tissues (2.4). In patients with index carcinomas of the colon and rectum, there were 142 clinically apparent, multiple primary cancers in other organs or tissues, or 1.4 times the expected number. After combining the experiences of patients with colon and rectal cancer, the incidence of breast cancer was significantly increased. In the patients with carcinoma of the rectum and rectosigmoid junction, the incidence of carcinoma of the urinary bladder was significantly, but inexplicably, increased. In those patients with carcinoma of the colon, the observed-to-expected ratio for carcinoma of the female genital organs was 2.1—primarily attributable to carcinoma of the endometrium. When the experience of 843 patients with endometrial carcinoma as their index cancer was considered, the increases in the observed number of associated and subsequent multiple primary cancers were similar for the large intestine, ovary, and breast. Similarly, in 921 index patients with primary ovarian carcinoma, there were 2 observed second primary cancers of the large intestine; this twofold excess was confined to the colon. These estimates of increased risk, which relate to multiple primary cancers of the large intestine, bladder, breast, and reproductive organs, have relevance both to the periodic examination of high-risk patients and to the epidemiologic pursuit of common etiologic factors.