Different apoptotic activity and p21WAF1/CIP1, but not p27Kip1, expression in serrated adenomas as compared with traditional adenomas and hyperplastic polyps of the colorectum

Purpose. Serrated adenomas (SAs), which include a wide spectrum of lesions, can be broadly divided into two subtypes: type I, closely mimicking hyperplastic polyps (HPs), and type II, unequivocal adenomatous tumor. Our preliminary findings showed clinicopathologic differences between them. The present study was conducted to investigate apoptotic activity and expression of the cell cycle regulator proteins p21(WAF1/CIP1) and p27(Kip1) in type I and II SAs, as compared with traditional adenomas (TAs) and HPs. Methods. Apoptotic activity was estimated in hematoxylin-eosin stained specimens, and p21(WAF1/CIP1) or p27(Kip1) immunoreactivity was determined in 62 SAs (19 type I and 43 type II), 50 TAs and 19 HPs. The numbers (percentages) of apoptotic or immunoreactive cells were counted per 1,000 epithelial cells in equally separated crypt zones (upper, middle, and lower thirds). Results. The apoptotic activity in the middle, but not the upper or lower crypt zone was higher in type II SAs (median 0.2%, interquartile range 0.1-0.5%) than in HPs (0.1%, 0.1-0.2%, P<0.01), whereas it was lower in type I SAs (0.2%, 0.1-0.3%) than in TAs (0.5%, 0.2-0.6%, P<0.001). P21(WAF1/CIP1) expression in the lower crypt zone was higher in both type I and type II SAs (19.8%, 7.0-33.2% and 20.4%, 3.9-47.8%, P<0.0001) than in TAs (1.2%, 0.6-5.2%), and a similar tendency was also observed for the middle crypt zone. p27(Kip1) expression did not vary among the groups. Conclusions. The differences in apoptotic activity and p21(WAF1/CIP1) expression between SAs and TAs or HPs indicate that SA should be considered as a distinct subtype of colorectal neoplasm. The two subtypes of SA do not differ in these parameters despite specific clinicopathological features.