While most (75.7%) of the substitutions targeting Cs were in the region spanning 1,200–2,200 bp (Fig. 1D), 6.5% of all substitutions in the T antigen area caused an in-frame stop codon (Table 1), and the in-frame stop codon distribution (Fig. 1E) explains only a very small proportion of the overall distribution of mutations in MCC samples (Fig. 1B). Here, CS is linked to Merkel cell skin cancer.