1. ¹Nuffield Department of Clinical Laboratory Sciences, University of Oxford, John Radcliffe Hospital, Oxford, UK
2. ²Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, Maryland

Correspondence: Joseph Geradts, M.D., Department of Pathology and Laboratory Medicine, Roswell Park Cancer Institute, Elm & Carlton Streets, Buffalo, NY 14263; e-mail: joseph.geradts@roswellpark.org; fax: 716-845-3427.

Accepted 21 July 2001.

Abstract

The INK4a locus encodes two structurally unrelated tumor suppressor proteins, p16^INK4a and p14^ARF. Although the former is one of the most common targets for inactivation in human neoplasia, the frequency of p14^ARF abrogation is not established. We have developed an immunohistochemical assay that allows the evaluation of p14^ARF expression in formalin-fixed, paraffin-embedded tissues, using commercially available antibodies. p14^ARF positive cells showed nuclear/nucleolar staining, which was absent in all cell lines and tumors with homozygous deletions of the INK4a gene. The assay was applied to 34 paraffin-embedded cell buttons, 30 non-small cell lung cancers and 28 pancreatic carcinomas, and the staining results were correlated with p16^INK4a expression. Loss of p14^ARF expression was common but less frequent than down-regulation of p16^INK4a (53% versus 76% of all specimens). The p14^ARF and p16^INK4a expression pattern was concordant in 65 of 92 cases (71%). Significantly, 24 cases were p16^INK4a-/p14^ARF+, while the opposite staining pattern was observed in three cases, consistent with the notion that the two proteins have nonredundant functions. The immunohistochemical assay described here may facilitate studies on the prevalence and significance of aberrant p14^ARF expression in human tumors.