The authors tested the hypothesis that alterations in tumor suppressor gene expression play a role in tumorigenesis of human soft tissue tumors through alterations in control of cell proliferation. Using a set of 66 soft tissue tumors, including benign tumors and all three grades of sarcomas, expression of the p53 and p110RB tumor suppressor gene products were localized using sensitive immunocytochemistry techniques. The hypothesis that alterations in tumor suppressor gene expression was related to cell proliferation was tested by simultaneously demonstrating the expression of the proliferating cell nuclear antigen in methacarn-fixed, paraffin-embedded tissue sections of the same tumors. Twenty-two of 66 (33%) and 35 of 68 (53%) tumors demonstrated any degree of p53 overexpression or loss of p110RB, respectively. A strong correlation between increasing tumor grade and both p53 overexpression (P = 0.006) and loss of p110RB (P = 0.003) was found. Although there was a correlation between increasing proliferating cell nuclear antigen index and overexpression of p53 (P = 0.04), no correlations were found between cell proliferation indices and loss of p110RB (P = 0.19). Finally, there was a significant correlation between the presence of immunocytochemically detectable p53 overexpression and detectable p110RB loss (P = 0.02). These studies suggest that although alterations in p110RB may play a role in soft tissue sarcoma tumorigenesis and be related to p53 dysfunction, p110RB may act through mechanisms other than direct loss of cell proliferation control.