To assess the spectrum of tumours induced by the expression of VAV1 gain‐of‐function mutations in cancer development, we used the CRISPR‐Cas9 gene editing technique (Fig. S1A) to generate mice bearing a Vav1 mutant allele encoding a CSH3‐truncated protein (amino acids 835–845, referred to hereafter as VAV1ΔC) (Fig. S1B). Here, VAV1 is linked to cancer.