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Molecular Oncology, Markers, Clinical Correlates |
Scheie Eye Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104 [M. M-G.]; Istituto di Clinica Oculistica, Seconda Universita degli Studi di Napoli, Naples 80131, Italy [G. B.]; and Departments of Pathology Anatomy and Cell Biology, Sbarro Institute for Cancer Research and Molecular Medicine, Jefferson Medical College, Philadelphia, Pennsylvania 19107 [A. D. L., A. B., A. G.]
| ABSTRACT |
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| INTRODUCTION |
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The retinoblastoma gene family is composed of three members: (a) the product of the retinoblastoma gene (pRb), which is one of the most well-studied tumor suppressor genes; and (b) two related proteins, pRb2/p130 and p107, which have been shown to be structurally and functionally similar to pRb (7, 8, 9) . The three retinoblastoma family members show growth suppressive properties, although the growth arrest mediated by each of the three pocket proteins is not identical (10 , 11) . This suggests that although the different members of the retinoblastoma gene family may complement each other, they are not fully functionally redundant. In a recent study of 71 lung cancers, using immunohistochemical techniques, we showed that these proteins display distinctive expression patterns when compared and contrasted to different parameters (12) . Additional studies on pRb2/p130 expression in lung cancer (13) and in endometrial carcinomas (14) point out a tight inverse correlation between tumor malignancy and pRb2/p130 expression, thus suggesting an involvement of this protein in the development and progression of these diseases. With this information as background, we studied the immunohistochemical expression of the pRb2/p130 gene as well as the other two members of the retinoblastoma gene family in a large number of samples of choroidal melanoma.
The distinct levels of expression of the three proteins in relation to patient survival, as well as the clinical significance of a lack of or a decrease in their expression in the course of choroidal melanomas, is discussed.
| MATERIALS AND METHODS |
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The histological diagnoses and classifications were performed using the Modified Callender Classification (3) , which contains three categories: (a) spindle cell melanomas; (b) mixed cell melanomas; and (c) epithelioid cell melanomas. All of the enucleated eyes had been formalin-fixed and sectioned along the longitudinal diameter, passing through the tumor and the optic nerve. The specimens were then processed through paraffin wax.
Immunohistochemistry.
Immunostaining for the retinoblastoma gene family members was performed using polyclonal antibodies ADL1 for pRb2/p130 and ADL2 for p107 and the monoclonal antibody XZ77 for Rb/p105 (12, 13, 14)
. The suitability for immunohistochemistry and the specificity of these antibodies have been described previously (12
, 13)
. The APAAP4
conventional method was used as the final chromogene, and hematoxylin was used as the nuclear counterstain. The results were evaluated independently by three observers (G. B., A. B. and A. G.) and scored as follows based on the percentage of positive cells: (a) score 1, 030% positive cells; (b) score 2, 3060% positive cells; and (c) score 3, >60% positive cells. The level of concordance, which was expressed as the percentage of agreement among the three observers, was 94.5% (52 of 55 specimens). In the remaining three specimens, the score was obtained from the judgements of the two observers who were in agreement.
Statistical Analysis.
The Kaplan-Meier method (15)
was used to estimate disease-free survival curves according to the immunohistochemical expression of retinoblastoma gene family members. The event used as an end point was death. The statistical significance of the difference between groups was assessed by the Mantel-Cox and Breslow tests. Multivariate Cox proportional hazards models stratified by histotype were used to assess pRb2/p130 expression in relation to survival. Additional models that controlled for DNA ploidy, PCNA expression, and tumor size were also used.
| RESULTS |
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| DISCUSSION |
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The role of members of the retinoblastoma gene family as tumor suppressors is well known (7) . However, few studies have been reported dealing with altered patterns of Rb/p105, p107, and pRb2/p130 in some neoplasms. Altered pRb2/p130 expression in primary lung cancer has been associated with a high proliferative index and with advanced tumor stages (12 , 13) . Studies of endometrial carcinomas confirm a relationship between altered expression of pRb2/p130 and the clinical course of the neoplasm (14) . A recent study shows that the retinoblastoma members could be directly involved in the pathogenesis of human mesotheliomas (17) .
Furthermore, genetic alterations disrupting the nuclear localization of Rb2 in human cell lines and primary tumors have recently been documented (18) . Such mutations may reduce growth inhibition, probably due to insufficient levels of the protein in the nucleus. Furthermore, pRb2/p130 has been shown to have antiproliferative and tumor-suppressive potentials both in vivo and in vitro using a tetracycline-dependent overexpression system. A JCV-transformed tumor cell line injected into nude mice formed lesions that regressed in the presence of induced pRb2/p130 (19) . Similar results were obtained in a study investigating the effects of pRb2/p130 expression in c-erbB-2-overexpressing SKOV-3 tumor cells (20) .
Drawing on this background, the analysis of the expression of the retinoblastoma gene family members in choroidal melanomas was considered relevant. No statistically significant correlation was found between the expression of Rb/p105 and p107 and the clinical course of choroidal melanoma, at least in our group of specimens. The level of expression of Rb/p105 in these tumors was always very low, and the biological significance of this phenomenon remains unclear. However, when we statistically evaluated patient outcome and correlated it with pRb2/p130 expression, we found pRb2/p130 to be an independent prognostic factor correlating with the overall survival time of the patients. Moreover, we compared the expression of Rb2/p130 with that of other well-established indicators (DNA content, PCNA level, and tumor size), showing that pRb2/p130 expression was the most significantly related to survival.
These results, as noted previously, are in agreement with previous work on lung and endometrial cancers (12, 13, 14) . In the absence of a widely accepted prognostic marker for choroidal melanoma, demonstration of the prognostic value of a simple assay, such as the immunohistochemical analysis of pRb2/p130 status on routinely formalin-fixed, paraffin-embedded specimens, acquires a high value. However, additional studies are required for more accurate modeling of these data and to compare the prognostic value of pRb2/p130 immunodetection to other recently proposed markers, such as p53 (21) .
| FOOTNOTES |
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1 Supported by the Sbarro Institute for Cancer Research and Molecular Medicine and supported in part by NIH Grants CA60999 and PO1 NS36466 (to A. G.). ![]()
2 To whom requests for reprints should be addressed, at Scheie Eye Institute, 51 North 39th Street, Philadelphia, PA 19104. Phone: (215) 662-8100. ![]()
3 Present address: Campus BioMedico University, Rome, Italy. ![]()
4 The abbreviations used are: APAAP, alkaline phosphatase anti-alkaline phosphatase; PCNA, proliferating cell nuclear antigen. ![]()
Received 7/29/98; revised 2/22/99; accepted 2/24/99.
| REFERENCES |
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