Meta-analysis finds germline LTS and somatic TERT variants are mutually exclusive in thyroid cancer and melanoma

Importance: Non-medullary thyroid cancer (NMTC) and melanoma are associated with inherited long telomeres due to germline pathogenic/likely pathogenic variants (PV/LPV) in POT1, TINF2, and ACD resulting in long-telomere syndrome (LTS) and they commonly have somatic TERT promoter mutations. The genetic relationship between these variants and their clinical associations are defined incompletely and may inform clinical practice. Objective: To test the hypothesis that germline LTS-associated PV/LPV are exclusive from functional somatic TERT variants and assess clinical/genetic associations. Design: Retrospective observational cohort study with/without germline LTS variants, that have somatic sequencing and pathology data. Setting: Participants were enrolled through 18 cancer centers participating in the Oncology Research Information Exchange Network (ORIEN). Participants: 995 adults with NMTC and 993 with melanoma between 2013 and 2025. All adult patients at an ORIEN center were offered enrollment Exposures: All patients with NMTC or melanoma are included. There are no required exposures. Main Outcomes and Measures: The presence/absence of a germline or somatic long-telomere variant; secondary outcomes are associations with tumor stage, telomerase expression, and oncogenes. Results: Germline and somatic variants in POT1/TINF2/ACD, somatic TERT promoter variants, TERT fusions, oncogenes, and telomerase mRNA expression were evaluated in 995 NMTC and 993 melanoma patients. In NMTC, 13 (1.5%) had a germline LTS variant while 0/12 with tumor sequencing had somatic TERT promoter variants/fusions. In melanoma, 7 (0.7%) had a LTS variant; 0/2 with tumor sequencing had a TERT promoter variant/ fusion. Meta-analysis including NMTC and melanoma in the current study, a recent thyroid cancer study, and thyroid TCGA, germline LTS-associated PV/LPV and somatic TERT variants/fusions were mutually exclusive (p=0.036). High telomerase mRNA levels were associated with TERT promoter variants/fusions (p<4e-11) and larger NMTC/distant metastases (p=0.016), but not germline LTS variants. NMTCs with somatic TERT promoter variants/fusions had higher tumor mutation burden (p<0.02) versus tumors from patients with a germline LTS variant. TERT promoter mutant variant allele frequency was lower in smaller and non-metastatic vs larger/metastatic NMTC. Conclusion and Relevance: Germline LTS-associated variants appear to be exclusive from somatic TERT promoter variants/fusions but are not associated with aggressive NMTC, suggesting common roles in tumorigenesis but different biological impacts.