The efficacy of HEI3090 to inhibit lung fibrosis was evaluated histologically on the whole lung’s surface by evaluating the severity of fibrosis using three independent approaches applied to the whole lung, the Ashcroft score, quantification of fibroblasts/myofibroblasts (CD140a) and polarized light microscopy of Sirius Red staining to quantify collagen fibers. The gene discussed is PDGFRA; the disease is fibrosis.