BACKGROUND: Many oncogenes have been recently identified in human thyroid carcinomas, but the molecular mechanisms that lead to thyroid neoplasia are not well understood. To assess whether oncogene- encoded proteins can be regarded as useful prognostic indicators, we have evaluated the expressions of c-met, c-Ha-ras, c-myc oncogenes in patients with papillary thyroid cancer (PTC) in relation to the prog nostic factors. METHODS: We used immunohistochemistry to examine the expressions of c-met, c-Ha-ras, and c-myc oncogenes in 54 paraffin-embedded PTC specimens. We measured both the proportion (scale of 0-3) and the intensity (scale of 0-3) of the stained cells and then calculated the staining index (scale of 0-9) by multiplying the proportion and the intensity scores. The staining index was thus categorized as negative/low (staining index < or =5) or high (staining index >5). The considered prognostic factors were age (over 45), tumor size (over 1.5 cm), lymph node metastasis, capsular invasion, vascular invasion, and distant metastasis. RESULTS: 1) The rates of expression of c-met, c-Ha-ras, c-myc oncogenes were 100%, 81.5%, and 70.3% in papillary thyroid cancer and 100%, 30%, and 10% in benign tumors and 60%, 10%, and 0% in normal thyroid tissue, respectively. The expression of c-met oncogene was restricted to the membrane the expression of c-Ha-ras was stromal in 95.5% of the specimens, and that of c-myc was stromal in 94.7%. 2) High expression (staining index >5) of c-met, c-Ha-ras and c-myc were not associated with the prognostic factors such as age, tumor size, lymph node metastasis, capsular invasion, vascular invasion and distant metastasis. CONCLUSION: Although the rates of expression of c-met, c-Ha-ras, and c-myc oncogenes were high in papillary carcinomas (100%, 81.5%, and 70.3%, respectively), there was no relationship between the high expression rates of the oncogenes and prognostic factors.