TERT and maternal uniparental disomy of chromosome 20: In our study, MBCs harboring TERT genetic alterations had a tumor mutation burden (median 3.1 mutations/Mb; range 0.8–6.1) comparable to that of MBCs lacking genetic alterations affecting TERT (median 3.5 mutations/Mb; range 0.8–8.7; p = 0.72, Mann–Whitney U test; Supplementary Fig. S2a).