ARID1A and granular cell tumor: In previous studies, we demonstrated that treatment of (cisplatin‐resistant) GCT cell lines with the histone deacetylase inhibitor (HDACi) romidepsin (ISTODAX, FR228, FR901228) efficiently induced apoptosis and blocked the cell cycle at very low doses, but did not affect survival of fibroblasts or Sertoli cells.4, 5, 6 We showed that romidepsin treatment of GCT cell lines resulted in heterochromatin formation within the promotor of ARID1A causing down‐regulation of ARID1A,5 which is a subunit of the chromatin remodelling SWI/SNF‐complex.