Lundberg A, et al. - Researchers performed comprehensive long-term survival analyses to determine the utility of cyclin D1 (CCND1) gene amplification for prognostication and treatment prediction in breast tumours. They used SNP arrays from two cohorts of 1965 and 340 patients to evaluate CCND1 amplification. Matching gene expression array and clinical follow-up data of over 15 years were also analyzed. They compared survival between CCND1 amplified vs non-amplified tumours by using Kaplan-Meier and multivariable Cox regression analyses. This was determined in clinically relevant patient sets, within PAM50 subtypes and within treatment-specific subgroups. In oestrogen receptor alpha +/lymph node −/human epidermal growth factor 2−, luminal A and luminal B patients, a worse 15-year survival was observed in relation to CCND1 amplification. Gene expression changes seen in luminal A CCND1-amplified tumours were consistent with a more aggressive phenotype. Patients that could benefit from long-term treatment strategies could be detected with CCND1.