Proliferating cell nuclear antigen/cyclin expression in small adenomas of the large intestine in relation to size and macroscopic appearance.

Sixty-two colorectal adenomas 10 mm or less in diameter, resected endoscopically and fixed in formalin for 3 days or less, were evaluated with antiproliferating cell nuclear antigen/cyclin (PCNA) monoclonal antibody to investigate the cell proliferation kinetics. All lesions were tubular adenoma with low-grade atypia. These lesions were classified by macroscopic type as: I; polypoid (n = 14), IIa; flat or hemispherically elevated (n = 28), IIb; plain, flat (n = 6), IIc; depressed (n = 9), and IIa+IIc slightly elevated with a central depression (n = 5). The distribution patterns of PCNA-positive cells were divided into two types; diffuse distribution of positive cells throughout the crypts (diffuse type) and localized distribution, mainly in the upper portions of the crypts (superficial type). The distribution pattern of proliferating cells was correlated with the size and macroscopic type of adenoma. Type IIc, IIa+IIc, IIb, smaller (< or = 5 mm) IIa and smaller (5 mm) I adenomas showed the superficial type pattern. Larger (> 5 mm) adenomas of type I and IIa had the diffuse type pattern. The formation of a proliferative zone in small adenomas, as in normal mucosa, but in opposite locations, suggested a lower cell proliferation activity. In the elevated type (I and IIa) adenomas, however, the change in the distribution pattern of proliferating cells from the superficial to the diffuse type would lead to growth in size.