PTEN and Egr-1 expression in thyroid proliferative lesions.PTEN is a tumor suppressor gene that inhibits cell cycle progression. Recent data support that PTEN transcription is upregulated by Egr-1. The present study evaluated the immunohistochemical expression of PTEN and Egr-1 in normal thyroid and in its benign and malignant proliferative lesions. PTEN expression was cytoplasmic. The median percentage of normal cells with positive staining was 97.5%. It was similar in nodular hyperplasia, adenoma and papillary carcinoma. Follicular and undifferentiated carcinoma presented a significant decrease in the percentage of positive cells (P=0.027 and P=0.004). Egr-1 expression was nuclear. The median percentage of positivity was similar in normal tissue (29.75%), nodular hyperplasia (30.5%) and papillary carcinoma (28.25%). Adenomas, follicular carcinomas and undifferentiated carcinomas showed a significant decrease of nuclear positivity (P=0.001; P=0.001 and P=0.004, respectively).