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.