Anatomic Pathology / Carbonic Anhydrase IX in Renal Tumors

Carbonic anhydrase IX (CAIX), a hypoxiainduced protein, is expressed in some renal tumors. We evaluated its immunohistochemical expression in 317 primary and 42 metastatic renal neoplasms (186 clear cell, 52 papillary, 35 chromophobe, 47 unclassified, and 15 Xp11.2 translocation renal cell carcinomas [RCCs]; 26 oncocytomas; 2 metanephric adenomas; 1 urothelial carcinoma; 1 mixed epithelial and stromal tumor; and 1 angiomyolipoma); 7 neoplasms were unknown as to whether they were primary or metastatic. We also correlated expression with tumor type and grade. Variable staining was seen in clear cell, papillary, unclassified, and Xp11.2 translocation carcinomas. One chromophobe carcinoma had focal expression. No staining was seen with other tumors. An association was found between high expression and clear cell vs non–clear cell carcinomas with all cases (P < .01) and primary (P < .01) cases. An association between CAIX expression and grade (P < .01) in primary clear cell carcinomas was found. CAIX expression is more common in clear cell RCC than other renal tumor types and is associated with grade. Renal cell carcinomas (RCCs) account for the majority (90%) of epithelial neoplasms of the kidney and 3% and 4% of new cancer cases in women and men, respectively.1,2 Of all RCCs, the clear cell subtype is the most common and accounts for the majority of RCC metastases.3 At diagnosis, up to 30% of patients will have metastases, and of patients who undergo nephrectomy for organ-confined disease, metastases will later develop in approximately 30% to 50%.2,4-6 Approximately, 13,000 patients die of the disease each year in the United States.2 The wide spectrum of histologically different tumor types and limited therapeutic options for systemic disease present distinctive challenges to physicians in terms of proper diagnosis and classification of these neoplasms and management of advanced disease. Renal epithelial neoplasms are unique in that their morphologic features are highly variable in terms of growth pattern and cytologic features, and there is morphologic overlap among the tumor types. Even within individual tumor types, especially clear cell RCC and papillary RCC, the morphologic features of one tumor to the next can be quite different. Nevertheless, routine H&E-stained sections are usually sufficient to correctly classify renal neoplasms. In some circumstances, however, the proper classification of primary renal tumors and distinguishing metastatic RCC from tumors that arise elsewhere can be problematic. Further compounding the issue are core biopsy specimens, which are not infrequently small and fragmented. Biopsies may be performed on tumors at metastatic sites or on renal tumors of patients who are not surgical candidates. In recent years, multiple immunohistochemical markers have been studied and offered as tools to distinguish Upon completion of this activity you will be able to: • define the most common primary and metastatic variant of renal cell carcinoma. • describe carbonic anhydrase IX and list the renal tumors that demonstrate immunoreactivity for it. • describe the reasons for the difficulties encountered in classifying primary renal neoplasms and treating the metastases. The ASCP is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The ASCP designates this educational activity for a maximum of 1 AMA PRA Category 1 Credit TM per article. This activity qualifies as an American Board of Pathology Maintenance of Certification Part II Self-Assessment Module. The authors of this article and the planning committee members and staff have no relevant financial relationships with commercial interests to disclose. Questions appear on p 1008. Exam is located at www.ascp.org/ajcpcme. Downloaded from https://academic.oup.com/ajcp/article-abstract/134/6/873/1760422 by guest on 27 July 2018 874 Am J Clin Pathol 2010;134:873-879 874 DOI: 10.1309/AJCPPPR57HNJMSLZ © American Society for Clinical Pathology Genega et al / Carbonic Anhydrase IX in Renal Tumors the various renal neoplasms from each other and from morphologically similar nonrenal tumors.7-11 No one marker has been found to be entirely specific for RCC in general or for any specific type of RCC. Carbonic anhydrase IX (CAIX) is one such marker that shows expression in RCC.12-14 CAIX is a hypoxia-induced protein that has a role in regulating intracellular and extracellular pH.14,15 Liao et al13 first reported expression of CAIX in clear cell RCC. Several years later, Bui et al16 found high expression of CAIX in clear cell RCC and, furthermore, reported that decreased levels of expression of CAIX were independently associated with poor outcome in advanced RCC. This latter observation has been refuted by other investigators.17 Atkins et al,18 among others,16 found that CAIX shows promise as a marker for selecting patients with advanced disease who would benefit from certain specific systemic agents, specifically interleukin-2 (IL-2). We undertook this study to assess the expression of CAIX in a variety of benign and malignant primary renal neoplasms and in RCC metastases. We sought to determine if CAIX could be used as an immunohistochemical marker to reliably distinguish among different tumor types and if its expression correlated with RCC grade. Materials and Methods All research involving human subjects was conducted on anonymized tissues obtained from patients during the course of their therapy. This research was approved by the Dana Farber/Harvard Cancer Center (DF/HCC) and the Beth Israel Deaconess Medical Center (BIDMC) institutional review boards (both Boston, MA). The study group consisted of primary and metastatic renal neoplasms mostly retrieved from the surgical pathology files at 3 institutions, including Brigham and Women’s Hospital, Boston; the BIDMC; and The Johns Hopkins Medical Institutions, Baltimore, MD. In addition, tumors resected at other institutions and stored at the DF/HCC Kidney Center SPORE tumor bank were also analyzed. The classification of the tumors from Brigham and Women’s Hospital, BIDMC, and the DF/HCC Kidney Cancer SPORE tumor bank was recorded from review of H&E-stained slides by 2 pathologists (E.M.G. and S.S.) or from pathology reports when all slides were not available for review. The Fuhrman grading system19 was used to grade RCCs. A coinvestigator from The Johns Hopkins Medical Institutions contributed 15 cases of Xp11.2 translocation RCC. CAIX immunostaining was performed on 1 representative section of tumor from each case in a DAKO autostainer system (DAKO, Carpinteria, CA). Sections were deparaffinized, soaked in alcohol, and, after microwave treatment in antigen unmasking solution for 10 minutes, incubated in 3% hydrogen peroxide for 15 minutes to inactivate endogenous peroxidase. Slides were then incubated with the mouse monoclonal antibody MN-75 (1:10,000 dilution), and detection was performed using the DAKO LSAB+ detection kit (DAKO). Semiquantitative assessment of the antibody staining for each slide was performed by 2 pathologists (E.M.G. and S.S.) who were blinded to the clinicopathologic variables of each case. Each specimen was scored based on the percentage of positive cells. As previously described,16,18 specimens in which more than 85% of tumor cells stained for CAIX were labeled as high-CAIX-expressing tumors, whereas those in which 85% or fewer tumor cells stained for CAIX were labeled as low-CAIX-expressing tumors. Fisher exact tests were used to determine the association between CAIX expression and tumor type and Fuhrman grade. Statistical significance was set at a P value of .05 or less.