DNA ploidy pattern of flat adenomas of the large bowel.

In an attempt to clarify the nature of "flat adenomas," DNA content was measured by means of microspectrophotometry. Thirty-nine flat adenomas (FA), 13 with mild, 22 with moderate, and 4 with severe atypia, were collected for this study. In FA, diploidy (D), polyploidy (P), and aneuploidy (A) were found 100, 0, and 0 percent in mild atypia, 41.9, 4.5, and 54.5 percent in moderate atypia, and 0, 0, and 100 percent in severe atypia, respectively. It is assumed that FA have a much higher malignancy potential than previously expected since, histologically, benign-appearing FA with moderate atypia have already contained malignant DNA patterns. In particular, those more than 5 mm in diameter show aneuploidy in 80 percent. These data suggest that FA with moderate atypia play an important role in the pathogenesis of small colonic carcinomas.