The present study clearly demonstrated that the frequency and the degree of PPARγ expression were significantly decreased as lesions progressed from a borderline tumour to carcinoma, and those of COX-2 expression were significantly increased as lesions progressed from a benign tumour to carcinoma, suggesting that low expression of PPARγ and high expression of COX-2 in precancerous lesions might be involved in progression of ovarian tumours to carcinoma. This evidence concerns the gene PTGS2 and carcinoma.