Surprisingly, despite the absence of NOX4 in stromal cells, tumours from WT and NOX4-/- mice were identical in size and in the expression levels of Krt19, α-Sma (Acta2) and collagen 1 (Col1a1) (Fig. 5a, b and Supplementary Fig. 19a). The gene discussed is ACTA1; the disease is neoplasm.