OBJECTIVETo investigate the clinicopathological characteristics and expression status of Ki67, p53, CEA, CDX, CK7 in colorectal sessile serrated adenoma (SSA).

METHODSThe clinicopathological data of 11 cases of SSA, 51 cases of hyperplastic polyp (HP) and one case with mixed HP/SSA were reviewed and analyzed retrospectively. The expression of Ki67, p53, CEA, CDX and CK7 were detected by immunohistochemistry.

RESULTSThe major histological features in SSA were architectural abnormality in crypts, dilatation of serrated crypt bases like an inverted "T" or "L" shape adjacent to muscularis mucosa. Atypical cells containing round to oval nuclei and nucleoli were also observed. The immunohistochemical staining showed that the expression of p53 increased gradually from HP to TA: 11.8% in HP, 20.0% in SSA, 41.2% in VTA and 75.0% in TA, with a significant difference among the groups (chi(2) = 17.996, P = 0.000). However, no significant difference in the expression of CDX and CK7 was observed between HP and SSA. Of the 10 SSA cases, positive expression of Ki67 was found in cells located in the base or middle part of crypt in 6 cases, positive cells index was 26% - 50% in 5 cases, and > 50% in 3. Compared with the expression of Ki67 in the HP, VTA and VA, SSA showed a significant difference in both the positive cell number and in the positive regions. (positive number: chi(2) = 34.601, P = 0.000; positive regions: chi(2) = 63.077, P = 0.000).

CONCLUSIONMorphological diagnosis of SSA was mainly based on crypt architectural and cellular abnormalities, and the crypt architectural abnormality may be more important than cellular features. Detection of p53 and Ki67 expression may be helpful in differential diagnosis and understanding the nature of SSA.