Expression of Rb2/p130 in breast and endometrial cancer: correlations withhormone receptor status

Rb2/p130 is a member of the retinoblastoma family of proteins, consisting o f Rb, Rb2 and p107, which are important negative regulators of cell cycle p rogression and differentiation. While Rb2 downregulation was observed in se veral malignant tumours including endometrial cancer, the role of p130 in b reast carcinomas is still unknown. We investigated Rb2 protein expression i n tumour tissue from 68 mammary and 41 endometrial carcinomas, 4 mammary ce ll lines, and normal tissue samples. Therefore, we performed Western blot e xperiments for Rb2, Rb, and the oestrogen and progesterone receptors (ER, P R-A, PR-B). Weak or absent Rb2 expression was more often found in endometri al (59%) than in mammary carcinomas (24%). We found significant positive co rrelations of Rb2 expression with Rb, ER, and PR-B in breast cancer samples , and of Rb2 with Rb, PR-A, PR-B, and younger age in endometrial carcinomas . No significant associations with histological grading, stage, nodal invol vement, or Ki67 staining were detected. Rb2 mRNA expression was studied by semiquantitative RT-PCR in 56 endometrial or mammary tissue samples and cor related significantly with Western blot results. Our results indicate that loss of Rb2 expression, mostly by transcriptional down-regulation, may be a ssociated with the development and dedifferentiation of most endometrial an d a subset of mammary carcinomas. (C) 2001 Cancer Research Campaign.