Is there loss or qualitative changes in the expression of thyroid peroxidase protein in thyroid epithelial cancer?

There is disagreement concerning the expression of thyroid peroxidase (TPO) in thyroid cancer, some studies finding qualitative as well as quantitativ e differences compared to normal tissue. To investigate TPO protein express ion and its antigenic properties, TPO was captured from a solubilizate of t hyroid microsomes by a panel of murine anti-TPO monoclonal antibodies and d etected with a panel of antihuman TPO IgG kappa Fab. TPO protein expression in 30 samples of malignant thyroid tissue was compared with TPO from adjac ent normal tissues. Virtual absence of TPO expression was observed in 8 cas es. In the remaining 22 malignant thyroid tumours the TPO protein level var ied considerably from normal to nearly absent when compared to normal thyro id tissue or tissues from patients with Graves' disease (range less than 0. 5 to more than 12.5 mug mg(-1) of protein). When expressed TPO displayed si milar epitopes, to that of TPO from Graves' disease tissue. The results obt ained by the TPO capturing method were confirmed by SDS-PAGE and Western bl ot analysis with both microsomes and their solubilizates. The present resul ts show that in about two-thirds of differentiated thyroid carcinomas, TPO protein is expressed, albeit to a more variable extent than normal; when pr esent, TPO in malignant tissues is immunologically normal. (C) 2001 Cancer Research Campaign.