Wilm's tumour gene, WT1

The WT1 protein is encoded by the WT1 gene located on chromosome 11p1315 and has four protein isoforms27. It encodes a 4 zinc finger protein that binds to the same DNA sequences as does ERG-111. While ERG-1 activates transcription, WT1 suppresses transcription. The suppressor function is lost in mutations that affect the zinc finger region11. Candidate target genes for WT-1 include e-cadherin and bcl-2, and there is interaction with p5321.

Germline deletion of one WT-1 allele, along with the neighbouring PAX6 gene, occur in the WAGR syndrome (Wilms tumour, aniridia, genitourinary abnormalities and mental retardation)19. In the Denys-Drash syndrome, there is a missense mutation effecting zinc finger 3 or a or truncating mutation, resulting in Wilms tumour, nephropathy and genital malformation, but with partial penetrance19. A homozygous knockout mouse model fails to develop kidneys or gonads and has small heart and lungs with a incomplete diaphragm19.

Alternative RNA splicing results at least twenty four isoforms22 of WT1 with variation in the carboxy-end zinc finger region. Of two major isoforms, the -KTS form appears to mediate transcriptional activation of genes, while the +KTS form may be involved in mRNA processing23. This variety of isoforms might theoretically influence immunoreactivity of the polyclonal antibody C-19, which is directed at the carboxyl end. The monoclonal 6F-H2 is directed at the amino terminus13. The 6F-H2 antibody is reported to produce stronger homogeneous reactivity than the C-19 clone in serous ovarian tumours13, but to produce no immunoreactivity in desmoplastic small round cell tumours1.

Although WT-1 is expressed in Wilms tumour, only 10% of sporadic cases show WT-1 mutations19. There is commonly loss of heterozygocity in ovarian tumours21.

Immunohistochemical expression

The informative immunoreactivity is nuclear.

• the mesodermally derived tissue of the developing urogenital tract: fetal and adult kidney and developing ovary and testis show positivity19. The epithelia of the Fallopian tube and the ovarian surface are immunoreactive16, while endometrium and cervical epithelia are not14.

• breast epithelium and myoepithelium are positive but many carcinomas are negative, using antibody C-1920.

• fetal spleen

• non-germ cells of the gonads28

• fetal and adult28 mesothelium, and mesothelioma. Staining is reportedly weaker in post mortem specimens that in the corresponding ante mortem mesothelioma specimens2.

• The ovarian surface epithelium and ovarian inclusion cysts stain29. Ovarian adenocarcinoma is positive, most other adenocarcinomas are negative:

Where there is both peritoneal serous carcinoma and serous carcinoma within an endometrial polyp, they are concordantly negative for WT-1, suggesting that the peritoneal tumour is metastatic from the endometrial primary27:

• Wilm's tumour

• spleen and some leukaemias19

• desmoplastic small round cell tumour (DSRCT)16. The chimeric EWS-WT1 protein in DSRCT acts as a transcription factor1.

• Malignant melanoma.

It is NOT expressed by:

• Ewing's sarcoma / Primitive neuroectodermal tumour1.

• neuroblastoma

• rhabdomyosarcoma

Diagnostic utility

• differentiation of epithelial mesothelioma from adenocarcinoma

A systematic review of eight studies (consisting of 264 epithelioid mesotheliomas and 213 pulmonary adenocarcinomas) reported sensitivities and specificities of WT-1 for epithelioid mesothelioma of 77% and 96%31.

Further studies are needed to see whether the high rate of positivity in epithelioid mesothelioma obtained by Ordonez9 using a newly available monoclonal antibody can be reproduced. Note that WT1 is commonly expressed by serous carcinomas of the ovary6.

• Differentiation of desmoplastic small round cell tumour (DSRCT) which stains positively for WT1 protein from Ewing sarcoma / primitive neuroectodermal tumour

• Identification of the primary site of adenocarcinomas, being commonly positive in ovarian but negative in breast carcinoma10.

• Differentiation of ovarian and peritoneal from uterine serous carcinomas. One paper reports positivity in uterine as well as ovarian serous tumours; although staining is significantly stronger in ovarian tumours, overlap was thought to limit the diagnostic value21. Adjuvant therapies differ, uterine serous tumours being less responsive to cisplatin-based chemotherapy than are ovarian serous tumours13.

• WT1 has recently been proposed as a complementary marker for malignant melanoma.

References

1 Hill AD et al. WT1 staining reliably differentiates desmoplastic small round cell tumor from Ewing sarcoma/primitive neuroectodermal tumor. An immunohistochemical and molecular diagnostic study. Am J Clin Pathol 2000;114:345-353.

2 Roberts, F., McCall, A. E., Burnett, R. A. Malignant mesothelioma: a comparison of biopsy and postmortem material by light microscopy and immunohistochemistry. J Clin Pathol 2001;54:766-70.

3 Amin, K. M., L. A. Litzky, et al. (1995). "Wilms' tumor 1 susceptibility (WT1) gene products are selectively expressed in malignant mesothelioma." Am J Pathol 146(2): 344-56.

4 Kumar-Singh, S., K. Segers, et al. (1997). "WT1 mutation in malignant mesothelioma and WT1 immunoreactivity in relation to p53 and growth factor receptor expression, cell-type transition, and prognosis." J Pathol 181(1): 67-74.

5 Oates, J. and C. Edwards (2000). "HBME-1, MOC-31, WT1 and calretinin: an assessment of recently described markers for mesothelioma and adenocarcinoma." Histopathology 36(4): 341-7.

6 Ordonez, N. G. (2000). "Value of thyroid transcription factor-1, E-cadherin, BG8, WT1, and CD44S immunostaining in distinguishing epithelial pleural mesothelioma from pulmonary and nonpulmonary adenocarcinoma." Am J Surg Pathol 24(4): 598-606.

7 Foster, M. R., J. E. Johnson, et al. (2001). "Immunohistochemical analysis of nuclear versus cytoplasmic staining of WT1 in malignant mesotheliomas and primary pulmonary adenocarcinomas." Arch Pathol Lab Med 125(10): 1316-20.

8 Miettinen, M., J. Limon, et al. (2001). "Calretinin and other mesothelioma markers in synovial sarcoma: analysis of antigenic similarities and differences with malignant mesothelioma." Am J Surg Pathol 25(5): 610-7.

9 Ordonez, N. G. (2003). "The immunohistochemical diagnosis of mesothelioma: a comparative study of epithelioid mesothelioma and lung adenocarcinoma." Am J Surg Pathol 27(8): 1031-51.

10 Lee, B. H., J. L. Hecht, et al. (2002). "WT1, estrogen receptor, and progesterone receptor as markers for breast or ovarian primary sites in metastatic adenocarcinoma to body fluids." Am J Clin Pathol 117(5): 745-50.

11 Rauscher, F. J., 3rd, J. F. Morris, et al. (1990). "Binding of the Wilms' tumor locus zinc finger protein to the EGR-1 consensus sequence." Science 250(4985): 1259-62.

12 Lae, M. E., P. C. Roche, et al. (2002). "Desmoplastic small round cell tumor: a clinicopathologic, immunohistochemical, and molecular study of 32 tumors." Am J Surg Pathol 26(7): 823-35.

13 Goldstein, N. S. and A. Uzieblo (2002). "WT1 immunoreactivity in uterine papillary serous carcinomas is different from ovarian serous carcinomas." Am J Clin Pathol 117(4): 541-5.

14 Shimizu, M., T. Toki, et al. (2000). "Immunohistochemical detection of the Wilms' tumor gene (WT1) in epithelial ovarian tumors." Int J Gynecol Pathol 19(2): 158-63.

15 Goldstein, N. S., D. Bassi, et al. (2001). "WT1 is an integral component of an antibody panel to distinguish pancreaticobiliary and some ovarian epithelial neoplasms." Am J Clin Pathol 116(2): 246-52.

16 Hashi, A., T. Yuminamochi, et al. (2003). "Wilms tumor gene immunoreactivity in primary serous carcinomas of the fallopian tube, ovary, endometrium, and peritoneum." Int J Gynecol Pathol 22(4): 374-7.

17 Logani, S., E. Oliva, et al. (2003). "Immunoprofile of ovarian tumors with putative transitional cell (urothelial) differentiation using novel urothelial markers: histogenetic and diagnostic implications." Am J Surg Pathol 27(11): 1434-41.

18 Al-Hussaini, M., A. Stockman, et al. (2004). "WT-1 assists in distinguishing ovarian from uterine serous carcinoma and in distinguishing between serous and endometrioid ovarian carcinoma." Histopathology 44(2): 109-15.

19 Pritchard-Jones, K. and L. King-Underwood (1997). "The Wilms tumour gene WT1 in leukaemia." Leuk Lymphoma 27(3-4): 207-20.

20 Silberstein, G. B., K. Van Horn, et al. (1997). "Altered expression of the WT1 wilms tumor suppressor gene in human breast cancer." Proc Natl Acad Sci U S A 94(15): 8132-7.

21 Acs, G., T. Pasha, et al. (2004). "WT1 is differentially expressed in serous, endometrioid, clear cell, and mucinous carcinomas of the peritoneum, fallopian tube, ovary, and endometrium." Int J Gynecol Pathol 23(2): 110-8.

22 Scharnhorst, V., A. J. van der Eb, et al. (2001). "WT1 proteins: functions in growth and differentiation." Gene 273(2): 141-61.

23 Lee, S. B. and D. A. Haber (2001). "Wilms tumor and the WT1 gene." Exp Cell Res 264(1): 74-99. This study used clone 6F-H2.

24 Ramalingam, P., A. Malpica, et al. (2004). "The use of cytokeratin 7 and EMA in differentiating ovarian yolk sac tumors from endometrioid and clear cell carcinomas." Am J Surg Pathol 28(11): 1499-1505.

25 Pan, C. C., P. C. Chen, et al. (2003). "Expression of calretinin and other mesothelioma-related markers in thymic carcinoma and thymoma." Hum Pathol 34(11): 1155-62.

26 Chu AY, Litzky LA, Pasha TL, Acs G,Zhang PJ Utility of D2-40, a novel mesothelial marker, in the diagnosis of malignant mesothelioma. Mod Pathol 2005; 18:105-10

27 Euscher ED, Malpica A, Deavers MT, et al. Differential expression of WT-1 in serous carcinomas in the peritoneum with or without associated serous carcinoma in endometrial polyps. Am J Surg Pathol 2005; 29:1074-8

28 Gulyas M,Hjerpe A Proteoglycans and WT1 as markers for distinguishing adenocarcinoma, epithelioid mesothelioma, and benign mesothelium. J Pathol 2003; 199:479-87

29 O'Neill CJ, Deavers MT, Malpica A, et al. An immunohistochemical comparison between low-grade and high-grade ovarian serous carcinomas: significantly higher expression of p53, MIB1, BCL2, HER-2/neu, and C-KIT in high-grade neoplasms. Am J Surg Pathol 2005; 29:1034-41

30 McCluggage WG, Oliva E, Connolly LE, et al. An immunohistochemical analysis of ovarian small cell carcinoma of hypercalcemic type. Int J Gynecol Pathol 2004; 23:330-6

31 King JE, Thatcher N, Pickering CA, et al. Sensitivity and specificity of immunohistochemical markers used in the diagnosis of epithelioid mesothelioma: a detailed systematic analysis using published data. Histopathology 2006; 48:223-32

32 Carlson JW, Nucci MR, Brodsky J, et al. Biomarker-assisted diagnosis of ovarian, cervical and pulmonary small cell carcinomas: the role of TTF-1, WT-1 and HPV analysis. Histopathology 2007; 51:305-12

This page last revised 30.11.2007.

©SMUHT/PW Bishop