Telomerase activity signature score correlates to increased FL-TERT isoform percentage but decreased TERT_238.6 isoform percentage. FL-TERT isoform percentage (significant in 9/33 cancer types) had all positive correlations. TERT_238.6 isoform percentage had significant negative correlations in 14/33 cancer types and TERT_656.1 had significant positive correlations in 2/33 cancer types. β-TERT, αβγ-TERT, and γ-TERT isoform percentage had no significant correlations to signature score expression. Spearman correlations were computed and significance determined using a Bonferroni corrected p-value of <0.000216 (0.05/231 comparisons). Correlations were highlighted with colour only if significant, blue indicating a significant positive correlation, and red indicating a significant negative correlation. Spearman’s coefficients are displayed, and colour intensity also indicates the strength of correlation. Question marks (“?”) indicate no correlation could be computed between signature score and the respective TERT isoform.