Importantly, the tumours with such ‘hybrid’ features in the setting of BHD demonstrate germline mutations of the tumour suppressor gene folliculin (FLCN), and on morphology they typically show a mosaic (‘checkerboard’) pattern, with eosinophilic/oncocytic cells intermixed with variable clusters of cells with clear cytoplasm or cytoplasmic vacuoles (Figure 3A,B).1, 42. Here, FLCN is linked to Birt-Hogg-Dube syndrome.