FKBP4 and neoplasm: This finding suggested a role for FKBP51 in participating in transcriptional complexes regulating the synthesis of cyclin D. By double immunofluorescence experiments on formalin-fixed and paraffin-embedded CRC samples, Rotoli et al. found FKBP51 and Proliferating cell nuclear antigen (PCNA) protein exhibiting nuclear colocalization in the early S phase in malignant cells forming tumor nests [56].