Natural history of early colorectal cancer.

Since superficial tumors have been found, their peculiar pathologic features have evoked questions concerning their biologic behavior, their natural history. The aim of the present study was to elucidate the natural history of colorectal cancers (CRCs) including superficial cancers, using a retrospective radiologic method. Forty nine cancers that had had initial configurations of early cancer seen by previous radiography and that were examined pathologically were the subject of the present study. Growth speeds [doubling time (DT) calculation] and configurational changes at the various stages (invasion depth) were compared between polypoid growth (PG) and nonpolypoid growth (NPG). Growth speeds of mucosal cancer and submucosal cancer were also compared. The results showed that early CRC grows slowly (DT 31.2 months) when the cancer is limited to the mucosa. However, as tumors grow down to the submucosa, their growth speed accelerates (DT 25.8 months). The DT of these early cancers were longer than that of advanced cancers. The pathologic growth pattern (NPG or PG) of the CRCs did not affect the tumor growth speed. In respect to tumor configuration, when the tumor is limited to the submucosa the antecedent growth pattern may be easily deduced. It seems difficult, however, to know the initial growth patterns in advanced cancers because cancers with polyloid growth frequently change to a nonpolypoid growth pattern when in advanced stages. Among 32 advanced cancers, only 6 (19%) derived from IIc/IIc + IIa cancer. The most common (more than 70%) origin of advanced cancer seems to be IIa, Is, and Isp lesions. These results suggest that NPG cancers or superficial depressed cancers are not the main origins of advanced cancers, and that these cancer do not show extraordinarily rapid growth.