Apoptosis and bcl-2 oncogene expression in Wilms' tumor

Wilms' tumor (WT) usually has a good outcome, although a poor prognosis is often related to more advanced stages and anaplastic features. Apoptosis occurs with variable frequency in malignant tumors, and may have a role in reducing their growth rate. The bcl-2 proto-oncogene inhibits apoptosis, and the consequent increase in the number of cells may play a role in the development of tumors. The aim of this study was to analyze the role of apoptosis and bcl-2 expression in WT. Twenty-six resected WT specimens were studied; 12 patients had stage I tumor, 4 stage II, 5 stage III, 3 stage IV, and 2 stage V. Twenty-three tumors were classified as favorable histology (FH) and 3 as unfavorable (UH). The mean follow-up was 34 months; 22 patients were alive and 4 were dead (2 with FH: 1 stage III and 1 stage IV, and 2 with UH stages 4). Apoptosis was detected by the in-situ end-labelling technique; bcl-2 expression was detected by immunohistochemistry. An apoptotic index (AI) was calculated as the ratio of apoptotic to normal cells in each specimen. The AI was lower in higher tumor stages, with a significant difference between stages I and IV (P < 0.05). In cases with UH, Al was lower than in tumors with FH (P < 0.01). The AI was also lower in patients who died than in those who survived (P < 0.01). In all specimens no correlation between AI and bcl-2 expression was observed. Progression to advanced stages of WT and a poor prognosis f anaplastic tumors may be linked with disruption of the mechanisms that control apoptosis. Bcl-2 does not play a role as a regulator of apoptosis in WT, other oncogenes and tumor-suppression genes may be more involved in inhibiting apoptosis in WT.