Histopathologic characteristics of advanced colorectal cancer smaller than 2 cm in size

Screening for colorectal cancer results in an increased incidence of early detection and decreased mortality. Although small colorectal cancer with deep invasion or lymph node metastasis is sometimes encountered, there is no comprehensive study evaluating the histopathologic features of such tumours. The aim of this study was to clarify the characteristics of advanced colorectal cancer <2 cm in size.

Using a series of 317 patients who underwent surgery for colorectal cancer, pathologic features were compared among small advanced cancers <2 cm invading the muscularis propria or subserosa (T2, T3) or involving the lymph nodes (N1, N2) (n = 22), small early cancers <2 cm invading only the mucosa or submucosa (T1) without lymph node metastasis (N0) (n = 24), and ordinary advanced cancers> 2 cm (n = 271).

Small advanced cancers were clearly different from small early cancers in gross appearance, histological type, frequency of serosal invasion (18% vs 0%, P < 0.05), lymph node metastasis (36% vs 0%, P < 0.01), and concomitant adenomatous component (17% vs 48%, P < 0.05). Small advanced cancers, when compared with ordinary advanced cancers, were characterized by the grossly superficial type (14% vs 1%, P < 0.01) and absence of serosal invasion (82% vs 14%, P < 0.01) However, the two groups were not significantly different with regard to the frequency of lymph node metastasis (36% vs 53%), liver metastasis (5% vs 15%), and stage of the disease (Dukes' A and B; 64% vs 45%).

The results indicate that colorectal cancers, once they invade beyond the submucosa, have the same metastatic potential, irrespective of tumour size. The low frequency of concomitant adenoma implies de novo carcinogenesis of the small advanced cancers.