TK1 and neoplasm: In order to determine whether the disproportional increase of 18 F-FLT uptake in FL relative to its low cell proliferation might be related to error-prone DNA repair known to occur in FL, we stained tumour samples of the 22 patients for the DNA replication and repair markers PCNA, TK-1 and RPA1 in addition to the pure DNA replication marker MIB-1.