ACTA1 and neoplasm: In vivo, we carefully analysed the proliferation rate of α-SMA-positive fibroblasts in archived tissue from a previously published preclinical trial.28 Co-immunofluorescence staining revealed a proliferation rate of 2%–5% in α-SMA-positive cells in vehicle-treated KPC tumours, and this rate did not change on gemcitabine treatment (figure 6A, B).