Immunohistochemical Expression of WT1 in Malignant Melanomas and Melanocytic Nevi

Kim, Yeon Woong; Shin, Dong Hoon; Choi, Jong Soo; Bae, Young Kyung

Abstract

BACKGROUND
Malignant melanomas represent pigmented skin lesions and should be distinguished from melanocytic nevi. However, differential diagnosis of malignant melanomas and melanocytic nevi is often challenging. Wilms' tumor 1 (WT1) protein is a specific immunomarker of Wilms' tumor, and several studies revealed that various malignant tumors have WT1 expression.
OBJECTIVE
The purpose of this study was to evaluate the usefulness of WT1 staining for differentiating malignant melanoma from melanocytic nevi.
METHODS
We selected 50 cases of melanocytic nevi (12 cases of junctional nevi, 19 of compound nevi, and 19 of intradermal nevi) and 35 cases of malignant melanoma (7 cases of malignant melanoma in situ and 28 cases of invasive melanomas) from clinicopathologically proven cases in the Department of Dermatology of Yeungnam University Medical Center. Immunohistochemistry analysis of WT1 was performed, and the labeling index of WT1 expressions was measured.
RESULTS
The mean labeling indices of junctional nevi, compound nevi, intradermal nevi, malignant melanoma in situ, and invasive melanomas were 1.9%±2.8%, 23.6±21.2%, 25.7±23.5%, 5.7±5.2%, and 66.1±32.0%, respectively. The labeling index of malignant melanoma in situ was higher than that of junctional nevi. The labeling index of invasive melanoma was higher than those of compound nevus and intradermal nevus. When the WT1 cut-off point to distinguish melanomas from melanocytic nevi was 27.2%, the sensitivity and specificity were 68.6% and 74%, respectively. When a WT1 cut-off point of 75% was used, the sensitivity and specificity were 40% and 100%, respectively. The mean labeling indices of stages I, II, III, and IV malignant melanoma were 29.5%±30.4%, 68.8%±33.9%, 79.5%±6.4%, and 77.7%±18.8%, respectively, and those of Tis, T1, T2, T3, and T4 were 5.7%± 4.8%, 8.0%±0%, 69.5%±18.5%, 61.9%±28.6%, and 78.6%±30.0%, respectively.
CONCLUSION
WT1 staining could be a potential diagnostic tool for differentiating malignant melanomas from melanocytic nevi because the WT1 labeling indices of melanomas were significantly higher than those of melanocytic nevi. WT1 staining may be helpful in predicting the depth and prognosis of malignant melanomas.