To establish primary murine fibroblasts for in vitro and in vivo tumor microenvironment investigation, dermal fibroblasts were isolated from neonatal mice carrying either Ctnnb1fl/fl; Col1α2‐CreER (bcat/Fb) or Ctnnb1+/fl; Col1α2‐CreER (Fb) alleles for culture as described 24. The gene discussed is COL1A2; the disease is neoplasm.