Tamm-Horsfall protein is a marker of renal and extra-renal rhabdoid tumours.

A monoclonal antibody (MAb) to Tamm-Horsfall protein (THP) was used to stain 6 renal rhabdoid tumours (RRT) and 2 primary extra-renal rhabdoid tumours (E-RRT). One of the E-RRT was a tumour from the posterior fossa of a 3-year-old child and the other was a lump from the right side of the neck in an 18-month-old girl. Five of 6 RRT and both cases of E-RRT were positive for THP. Both cases of E-RRT also reacted with vimentin and cytokeratin MAbs. On electron microscopy, cells from both E-RRT were seen to contain concentric whorls of intermediate filaments characteristic of rhabdoid tumours. Viable tissues from one RRT and one E-RRT (the posterior fossa tumour) were available for tissue culture. Ninety-five percent of the cells growing out of both tumours were polygonal and approximately 5% of these cells were THP-positive.