Expression of retinoblastoma gene (Rb) protein in T12MO prostatic adenocarcinoma

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Abstract
The expression of Rb protein was analysed by immunocytochemical methods in 118 patients with T12M0 prostatic adenocarcinoma who were followedup for more than 12 years. Rb protein was expressed in 117/118 (99%) tumours. The fraction of positive nuclei was (mean±SD, 92±19%) and only one tumour was completely negative for Rb protein. Abnormal expression of the Rb protein (in fewer than 90% of cells) was independent of the T category while there was a significant relationship between DNA ploidy (P=0.0138), S-phase fraction (P=0.0042) and expression of the Rb protein. Abnormal expressin of the Rb protein had no prognostic value while T category (P=0.0017), Gleason score (P=0.0097), DNA ploidy (P=0.0034), S-phase fraction (P=0.0179) and mitotic index (P=0.0001) were significant prognostic factors. In multivariate analysis the only independent predictor was the mitotic index [Risk ratio (RR) (95%CI)=7.4(2.4–22.5),P=0.004]. The results show that Rb protein immunohistochemistry has hardly any prognostic significance in prostatic adenocarcinoma whereas direct measurement of cell proliferative activity contains significant prognostic information.