Inverse relationship between expression of PTEN and cytoplasmic localization of p21 in canine melanoma. A series of naturally occurring canine melanomas on which we previously reported expression of PTEN and p21 (see text) was re-examined to determine if there was a consistent relationship between expression of these proteins. Data were evaluated from tumors that had easily detectable PTEN staining in >30% of cells (1+, N = 9), weak expression of PTEN (required high magnification for confirmation) in >30% of cells (+/-, N = 9), or no expression of PTEN (-, N = 5). Each tumor was then examined for p21 intensity and subcellular localization. Data represent the % of samples that showed cytoplasmic p21 for each group. The numbers over each bar represent the sample size for each group; *p < 0.03 compared to PTEN(-).