METALLOTHIONEIN EXPRESSION IN RENAL CANCER JONATHAN I. IZAWA, MADELAINE MOUSSA, M. GEORGE CHERIAN, GORDON DOIG, AND JOSEPH L. CHIN ABSTRACT Objectives. To assess metallothionein (MT) expression with immunohistochemical localization in human renal cell carcinoma and to determine whether a possible relationship with the histopathologic findings, tumor grade, or pathologic tumor stage is demonstrable, because MT may have a role in carcinogenesis. Methods. Archival pathologic specimens and medical records were reviewed for 28 patients with renal cell carcinoma. Immunohistochemical localization of MT was performed with a polyclonal-antibody-to-rat-liver MT, an anti-rabbit IgG linking antibody, and an avidin-biotin horseradish peroxidase complex. Correlation was sought between immunohistochemical data (MT staining intensity, extension, and subcellular site) and clinical data (histologic cell type, tumor grade, and pathologic stage). Results. The mean patient age was 61.7 years (range 42 to 86). The predominant histologic cell type was the clear cell variant. Three, sixteen, and nine tumors were pathologically staged as 1, 2, and 3, respectively. There were 1, 13, 10, and 4 tumors with grades 1, 2, 3, and 4, respectively. Among the independent variables, greater immunoreactivity was observed in Stage 2 tumors (P = 0.028). A significant inverse relationship between tumor grade and MT staining intensity was also observed (P = 0.007). Conclusions. The inverse relationship in renal cell carcinoma between MT immunoreactivity and tumor grade may indicate a role for MT in tumor growth and dedifferentiation. Increased MT immunoreactivity in lower stage tumors may be related to rapid tumor growth during their growth cycle. Further study is required to elucidate the role of MT in renal cell carcinoma oncogenesis and its possible use as a clinical prognostic parameter. UROLOGY 52: 767–772, 1998. © 1998, Elsevier Science Inc. All rights reserved. M etallothionein (MT) was first discovered in 1957 as a cadmium and zinc binding protein in horse kidney. 1,2 Since then, similar proteins have been identified in many different tissues and cell types. MTs are now known to be a group of cysteine-rich, metal-binding proteins of low mo- lecular weight 3 that have a role in the detoxifica- tion of heavy metals. MT can be induced by heavy metal ions, such as cadmium, zinc, copper, and mercury. 4 It has been hypothesized that MT may play a role in carcinogenesis on the basis of the two basic properties of this protein. 5 First, MT genes are highly inducible, and second, MT is ubiqui- tous. Previous studies have shown that preinduc- tion of MT synthesis can protect against the toxic side effects of anticancer drugs, 6 and MT may have a role in the development of drug resistance in tumor cells. 7 Other possible functions include ho- meostasis of metals, which may be required for tumor cell growth and differentiation 8 ; detoxifica- tion of free radicals; and sulphur metabolism. MT synthesis is regulated by the rate of MT gene tran- scription, which in turn is mediated by interactions between upstream regulatory DNA sequences and unidentified cellular factors. 9 Glucocorticoids and products of the inflammatory response, such as catecholamines, interleukins, and interferon, are also known to induce MT gene transcription. 8 –10 Changes in gene structure such as amplification, methylation, and cellular differentiation and devel- opment can alter MT expression. 8 Previous studies have demonstrated expression of MT in various types of human tumors, including thyroid, 11 sali- vary gland, 12 testicular germ cell tumors, 13 urinary bladder tumors, 14 and prostate cancer. 15 The func- tional role of MT in renal cell carcinoma tumors is poorly understood. Therefore, we undertook this study to (1) evaluate the localization of MT in hu- From the Departments of Surgery, Division of Urology, Pathol- ogy, and Biostatistics and Epidemiology, The University of West- ern Ontario, London, Ontario, Canada Reprint requests: Joseph L. Chin, M.D., London Health Sciences Center, University of Western Ontario, 800 Commissioners Road East, London, ON N6A 4Y5 Canada Submitted: August 25, 1997, accepted (with revisions): May 4, 1998 ADULT UROLOGY © 1998, ELSEVIER SCIENCE INC. 0090-4295/98/$19.00 ALL RIGHTS RESERVED PII S0090-4295(98)00323-9 767