Loss or altered subcellular localization of p27 in Barrett's associated adenocarcinoma.

The cyclin-dependent kinase inhibitor p27 is a negative regulator of the cell division cycle. It is expressed at the highest levels during the quiescent (G0) and prereplicative (G1) phases, and its degradation is required for entry into the S phase. Because lack of p27 is associated with aggressive behavior in a variety of tumors of epithelial and lymphoid origin, we used immunohistochemistry and in situ hybridization to evaluate the expression of p27 in metaplastic and dysplastic Barrett's epithelium and to assess its prognostic significance in Barrett's associated adenocarcinoma (BAA) of the esophagus. In metaplastic Barrett's epithelium, p27 protein and mRNA were restricted to the superficial third of glands in all cases and extended to the lower third in 4 cases. In contrast, expression of p27 message and protein was both increased and full-thickness, in the 23 cases with high-grade dysplasia adjacent to BAA and in carcinoma in situ. Although all invasive carcinomas had elevated levels of p27 mRNA, 45 (83%) of 54 invasive carcinomas had low p27 protein levels (<50% positive tumor cells). Low p27 protein correlated with higher histological grade (P < 0.0001), depth of invasion (P = 0.0120), presence of lymph node metastasis (P = 0.05), and survival (P = 0.0197). In addition to the nuclear staining, cytoplasmic staining of p27 was noted in 11 of 23 (48%) of cases of dysplasia and in 14 of 54 (26%) adenocarcinomas and confirmed, in a subset of cases, by subcellular fractionation of protein lysates obtained from fresh tumor tissues. Cytoplasmic localization of p27 was also associated with decreased survival (P = 0.0239). Loss of p27 conferred poor prognosis independently of proliferative index, as assessed by Ki-67 (MIB-1) immunostaining, which was not significantly different in survivors versus nonsurvivors. These results show that: (a) distribution of p27 message and protein parallel one another in metaplastic and dysplastic Barrett's epithelium, suggesting transcriptional regulation of the gene in the nonneoplastic setting; (b) p27 is inactivated in the majority of BAA as a result of either post-transcriptional modification or altered subcellular localization; and (c) loss of the cell cycle inhibitor p27 is associated with parameters of aggressive behavior and unfavorable outcome in BAA.