Lastly, an adequate number of neoplastic biopsy samples is the basis of MMR testing, and we have shown that at least five samples is probably sufficient for testing (similarly to the biopsy numbers suggested for HER2 and PD-L1 testing in gastric cancer; Gullo et al. 2015; Grillo et al. 2013; Mastracci et al. 2022). Here, ERBB2 is linked to gastric cancer.