Mutations in the promoter region of the gene coding for the reverse transcriptase component of telomerase (TERT) are found at high frequency in various human tumor types. These TERT promoter mutations (TPMs) have been detected both in early- and late-stage tumors, consistent with the possibility that they play a role early in tumorigenesis. SAO-based imaging using the StellarVision instrument was used to obtain measurements of individual telomeres at the single-cell level across multiple whole tissue sections of melanomas arising from nevi. In all four cases tested, the authors found telomeres were significantly shorter in the melanoma than in the nevus, highlighting that in vivo TPMs do not induce TERT expression levels sufficiently to counteract or reverse telomere shortening.