Carcinoma of the large bowel in Singapore--a pathological study.

Five hundred and sixty-five cases of large bowel cancer were analysed. There were 8 (1.4%) appendiceal tumours, 296 (52.4%) colonic cancers, 236 (41.8%) rectal cancers, 6 (1.1%) anal cancers and 19 (3.4%) multiple primary cancers of the large bowel. Non-mucinous adenocarcinoma was by far the commonest histological type of large bowel cancer (74.7%). This was followed by mucinous carcinoma (20.7%). Other histological types were relatively uncommon. They included carcinoid tumours (1.8%), signet-ring cell carcinoma (1.5%), squamous cell carcinoma (0.7%), undifferentiated carcinoma (0.4%) and adenosquamous carcinoma (0.2%). The proportion of mucinous carcinoma was greater among the Indians and Malays than among the Chinese. There was a positive correlation between the grade and extent of spread of the tumour. The right colon had greater proportion of poorly differentiated adenocarcinomas than the left colon; this tendency was more evident in females. Mucinous carcinoma tended to occur more frequently in the younger age groups and in populations with low risk for colorectal cancer. Remnants of adenoma, often with a prominent villous component, were found to associate with mucinous carcinoma in a significantly higher proportion (18.0%) than non-mucinous adenocarcinoma (2.6%) (P less than 0.001). Papillary structures within the tumour were encountered in 26.2% of mucinous carcinoma compared to 13.4% of non-mucinous adenocarcinoma (P less than 0.001). A greater proportion of mucinous carcinoma was located in the caecum-ascending colon compared with non-mucinous adenocarcinoma. It is suggested that the histogenetic relationship with adenoma, particularly villous adenoma, was stronger in mucinous carcinoma than in non-mucinous adenocarcinoma. The relationship between the amount of mucin and the grade and stage of the cancer was not a linear one. In general, greater proportions of poorly differentiated and advanced tumours were encountered when the amount of mucin exceeded 50% of the tumour area. Multiple cancers of the large bowel increased with age. Compared with single cancers, they tended to be smaller, better differentiated, less extensive in their spread and had a stronger association with adenomas of the large intestine.