In addition to hematoxylin and eosin staining and histological comparison to the original tumour, the included studies validated the various models by examining preservation of key driver gene mutations, most commonly KRAS, BRAF and PIK3CA (9 studies); gene expression (8 studies); copy number variations (2 studies) and protein expression (predominantly via immunohistochemistry). The gene discussed is PIK3CA; the disease is neoplasm.