FOLR1 and neoplasm: FRα immunoreactivity score (0–8) was assessed by IHC in xenografted Skov-3 (4.6 ± 2.5) and A549 (2.7 ± 0.8) tumours (Fig. 4c), confirming an association between higher fluorescence intensities in Skov-3 tumours and higher target expression, which was also previously observed by flow cytometry and in vitro FLI (Fig. 2 and S18).