Clinicopathological analysis of invading muscularis propria (T2) cancers < or =20 mm in diameter.

Because the percentage of advanced colorectal cancers reportedly increases when colorectal cancers exceed 20 mm in diameter, it is important in elucidating the development and progression processes of colorectal cancer to analyze the clinicopathological and molecular genetic features of small advanced colorectal cancers. In this study, we analyzed the clinicopathologic and morphogenetic features and invasive capacity of small advanced colorectal cancers(T2) <20 mm in diameter in which cancer cells invaded the muscularis propria. The fresh surgical specimens examined consisted of 16 T2 cancers <20 mm in maximum diameter (small T2 cancers) and 52 T2 cancers >20 mm in maximum diameter (typical T2 cancers). Clinicopathologic analysis showed that 7 (44%) of the 16 small T2 cancers and 11 (21%) of the 52 typical T2 cancers metastasized to lymph nodes, with a tendency (P = 0.07) in frequency between small and typical T2 cancers. Morphogenetically, 63% of the small T2 cancers and 25% of the typical T2 cancers belonged to the nonpolypoid growth group. Fifty-six percent of the small T2 cancers and 48% of the typical T2 cancers expressed MMP-9. Morphogenetically, typical T2 cancers more frequently showed polypoid growth, whereas small T2 cancers more frequently showed nonpolypoid growth, indicating a different morphology between the two types of T2 cancers. The results of clinicopathologic analysis and examination of MMP-9 expression suggest that small T2 cancers have the same degree of malignancy as typical T2 cancers.