Immunohistochemistry staining for endogenous biotin within selected tumours (A, C, E) and their respective non-neoplastic negative surgical margins. A: Renal cell carcinoma (RCC), conventional type, GIII, 200 × magnification; B: Non-neoplastic surgical margin tissue adjacent to A, 200 × magnification; C: RCC, chromophobe, 200 × magnification; D: Non-neoplastic surgical margin tissue adjacent to C, 200 × magnification; E: transitional cell carcinoma, papillary type, Low grade, 100 × magnification to show the papillary architecture; F: Non-neoplastic surgical margin tissue adjacent to E, 200 × magnification.