ACTA1 and neoplasm: With an extensive population of fibroblasts that range from tumor-promoting and tumor-suppressing4, two main populations of fibroblasts have been defined by Ohlund et al.5 in 2017: pro-fibrotic myofibroblasts (myCAF) characterized by α-SMA (smooth muscle actin), and pro-inflammatory fibroblasts (iCAF) expressing high levels of interleukins.