B2M and neoplasm: Intratumour heterogeneity remains a considerable challenge, and it may be that combining DNA from multiple FFPE tumour blocks would be more effective for B2M testing, as demonstrated for KRAS.21 Deeper and more expansive ‘next‐generation sequencing’ approaches might also identify a higher proportion of B2M mutations among dMMR CRCs, but results with formalin‐fixed paraffin‐embedded (FFPE) specimens have been variable and would require careful validation.