By performing double immunofluorescence in TART cells, the authors found that a proportion of TART cells co-expressed both 11-β hydroxylase (adrenal-specific and encoded by the CYP11B1 gene) and 17β-Hydroxysteroid dehydrogenase 3 (Leydig cell-specific, encoded by the HSD17B3 gene) indeed indicating the presence of ‘hybrid’ cells with an adreno-testicular phenotype, rather than a heterogeneous population of separate adrenal-like and testicular-like cells within the tumour parenchyma. The gene discussed is HSD17B3; the disease is neoplasm.