Small, flat colorectal cancers in the UK population: an analysis of resected specimens

To establish the prevalence of small, flat carcinomas in surgically resected colon. To determine whether tumour morphology influences stage at presentation.

1763 surgically resected colorectal cancers from one UK centre excised between 1995 and 2004 were examined. Age 69 years, (42-90), M:F equal. Sixty-one tumours < or =20 mm across were identified. Slides were reviewed by a consultant histopathologist and classified using Japanese Research Society Classification, JRSC and TNM staging. Fisher's exact test was used for analysis.

In 61 small cancers, 64% (39/61) showed flat morphology and 33% (20/61) polypoid. Two lesions were unclassifiable. Prevalence was 2.2% of all resected colorectal cancers. More T1 tumours at presentation were polypoid, (30% vs. 8%; P = 0.033). T3 tumours were more likely to be flat than polypoid, (49% vs. 20%; P = 0.016). Infiltration into musclaris mucosa occurred in 77% (30/39) flat tumours. Rates of metastases were high in both groups, (30% polypoid vs. 39% flat, not significant).

The prevalence of small, flat cancers in resected specimens in the UK concurs with that of Japanese studies. Small, flat cancers should be staged carefully because of high rates of T3/4 disease. The results support the theory of accelerated carcinogenesis in flat cancers.