Abstract

Wilms' tumor is one of the most common primary malignant tumors of the kidney during infancy and childhood and is known to be originated from the primitive cells of metanephric blastema. It presents difficulties when encountered in deciding the presence of anaplasia or in differentiating it from other renal tumors of childhood with different biologic behavior because of its diverse histologic patterns and varying degrees of differentiation. Evaluation of clinical and histopathologic features in terms of prognostication was done of 32 cases of Wilms' tumor which were surgically resected and diagnosed in the period from January 1979 through June 1992. Immunohistochemical reaction for cytokeratin, vimentin, actin and desmin was also analysed on all cases of Wilms' tumor in conjunction with clear cell sarcoma of the kidney(CCSK), malignant rhabdoid tumor of the kidney(MRTK) and congenital mesoblastic nephroma(CMN) to assess the validity of immunohistochemistry in differentiating Wilms' tumor from these renal tumors. Twenty four(75%) cases were diagnosed before the age of 5 and 40.7% were under 2 years old. Mixed type was most common(62.5%), followed by epithelial, blastemal and stromal predominant type in descending order of frequency. Anaplasia was observed in 3 cases(9.4%), two of which were epithelial predominant type and one blastemal predominant type. Treatment modality and presence of anaplasia were significantly correlated with 5 year survival rate of patients. Immunohistochemical stain revealed that all epithelial component of Wilms' tumor were positive for cytokeratin and 56.3% of Wilms' tumor had blastemal component which were positive for both cytokeratin and vimentin. Twenty cases(62.5%) of Wilms' tumor had blastemal component which were positive for cytokeratin with a proportion of more than 5% of reactive cells. Stromal component of Wilms' tumor generally did not show differentiation into the specialized type of tissue and all revealed positive reactions for vimentin among which some revealed positive reactions for actin. Only 3 out of 6 cases with rhabdomyoblastic differentiation were positive for desmin. CCSK, MRTK and CMN which have different biologic behavior and treatment modality compared to Wilm's tumor showed positivity only for vimentin and/or actin. In summary, treatment modality and presence of anaplasia are significantly correlated with patients' survival and the immunohistochemical stain for cytokeratin is very helpful in confirming the presence of blastemal component and useful in the differential diagnosis of Wilms' tumor from other kinds of pediatric renal tumors.

• Keywords: Wilms' tumor;Anaplasia;Immunohistochemistry