NM_000051.4:c.1009C>T (p.Arg337Cys) is a missense variant in ATM exon 8. This variant is present in gnomAD v4.1 at an overall allele frequency of 0.00892% (144/1,613,688 alleles, 0 homozygotes) with a grpmax filtering allele frequency of 0.021% in the Admixed American population.¹ This variant does not meet PM2_Supporting (frequency ≤0.001% required), BS1 (>0.05% required), or BA1 (>0.5% required) under ATM VCEP population thresholds.² This variant has been reported in ClinVar (Variation ID 127327) as Uncertain Significance by 18 clinical laboratories and as Likely Benign by 3 clinical laboratories; no submitter classifies it as pathogenic.³ The variant has been reported 80 times in somatic cancers (COSMIC COSV53723836) and OncoKB classifies it as Likely Oncogenic with a loss-of-function effect in the somatic context.⁴ Computational predictors do not support a deleterious effect: REVEL score is 0.36 (VCEP PP3 threshold >0.7333, BP4 threshold ≤0.249), SpliceAI max delta is 0.10, and BayesDel is 0.067.⁵ The ATM VCEP functional dataset (Suppl_TableS1, PMID 40580951) classifies this variant as 'Functional' (combined score -0.65, high confidence) based on integrated functional and evolutionary scores, meeting BS3_Supporting under VCEP rules.⁶ PVS1, PS1, PS2, PM1, PM5, PM6, PP2, PP4, PP5, BS2, BS4, BP1, BP5, BP6, and BP7 are not applicable under ATM VCEP v1.5.0 for this variant type.⁷ No case-control study demonstrates enrichment of this variant in affected individuals (PS4 not met), and no segregation data are available (PP1 not assessed).⁸ With only BS3_Supporting met and no pathogenic criteria fulfilled, the evidence is insufficient to classify this variant as either likely benign or likely pathogenic; the variant remains a Variant of Uncertain Significance under the ATM VCEP framework.⁹