Expression of promyelocytic leukaemia protein in thyroid neoplasms

Promyelocytic leukaemia protein (PML) is an oncoprotein involved in the pathogenesis of acute promyelocytic leukaemia and is localized in distinct PML nuclear bodies. Our previous observation of overexpression of the PML in hormone-sensitive normal tissues and malignant solid tumours, including the thyroid, led to this analysis of the PML expression in various thyroid neoplasms to characterize the importance of the PML in thyroid carcinogenesis.

Immunohistochemistry was performed on paraffin-embedded tissue samples from 106 thyroid neoplasms after antigen retrieval by microwave. Immunoblotting was done with fresh frozen tissues in a few tumours. The PML was strongly expressed in all papillary carcinomas in diffuse or ball-shaped patterns. In the follicular neoplasms, the PML expression was variable, but there was no significant difference between adenomas and carcinomas. In the medullary carcinomas, the PML expression was either not detectable or was lower than in non-neoplastic thyroids. Quantitatively different expression of the PML in various thyroid neoplasms was confirmed by immunoblotting.

A significant difference of the PML expression according to the type of thyroid neoplasms suggests that the PML is important in papillary thyroid carcinomas, and furthermore, that PML expression may be used in differential diagnosis of thyroid neoplasms.