Immunohistochemical Expression of Retinoblastoma Gene Product in Normal, Hyperplastic and Malignant Endometrium. Correlation with p53 Protein Expression, c-erbB-2, Hormone Receptors’ Status and Proliferative Activity

Alterations of the retinoblastoma (Rb) gene have been described in several human neoplasms and recently, it has been suggested that these alterations may play a role in the development of endometrial carcinomas. Paraffin sections from 31 cases of normal endometrium (16 proliferative, 15 secretory), 35 hyperplastic lesions and 89 endometrial carcinomas were investigated immunohistochemically for Rb protein (pRb) expression. The results were compared with p53 and c-erbB-2 protein expression, estrogen (ER) and progesterone (PR) receptors' status and with clinicopathological prognostic factors. pRb was expressed in normal, hyperplastic and neoplastic epithelium. Proliferative endometrium showed more intense and extensive pRb staining than secretory endometrium. pRb reactivity was heterogeneous in the hyperplastic endometrial cells. Lack or focal (< 10% of endometrial cells) pRb immunostaining was noted in 56.2% and 27% of carcinomas, respectively. In the remaining cases (16.8%) pRb staining was heterogeneous or diffuse. The absence or presence of pRb expression was independent of grade and stage. In normal proliferative and secretory endometrium, pRb expression was correlated with PR (p = 0.006 and p = 0.001, respectively), PCNA (p = 0.04 and p = 0.01, respectively) and MIB1 (p = 0.02 and p<0.0001, respectively) expression. In hyperplasias, pRb was related to PR (p = 0.016) and MIB1 (p < 0.0001) expression. In carcinomas, a relationship of pRb expression with p53 (p = 0.0015), ER (p = 0.0002), PR (p = 0.0004) and PCNA (p = 0.013) status was detected. We suggest that the absence or presence of pRb expression does not seem to be associated with the progression of endometrioid carcinoma. In addition, pRb seems to be normally regulated in relation to the proliferative growth fraction of the tumours.