Lactate Dehydrogenase-to-Albumin Ratio and Glasgow Prognostic Score as Prognostic Markers in Metastatic Breast Cancer Treated with CDK4/6 Inhibitors

Background: CDK4/6 inhibitors with endocrine therapy are standard first-line treatment for hormone receptor-positive, HER2-negative metastatic breast cancer, yet simple pretreatment prognostic markers are lacking. The LDH-to-albumin ratio (LAR) and the Glasgow Prognostic Score (GPS) both incorporate serum albumin and are each reported as prognostic, but have not been compared within a single cohort, and LAR has not been examined during CDK4/6 inhibitor therapy. This study evaluated both indices in this setting. Methods: Consecutive patients (n = 139) receiving palbociclib or ribociclib plus endocrine therapy (2020–2025) were analysed retrospectively. LAR was modelled continuously on the logarithmic scale, with hazard ratios per doubling; an external cut-off (46.27) served for Kaplan–Meier illustration only. GPS was calculated in its original form. As both contain albumin, each entered a separate multivariable Cox model with identical covariates. Endpoints were overall survival (OS) and progression-free survival (PFS). Results: Over a median follow-up of 50.0 months, 72 deaths and 110 progression events occurred. LAR was independently associated with OS (adjusted HR 2.87 per doubling, 95% CI 1.78–4.62, p < 0.001) and PFS (2.21, 1.45–3.35, p < 0.001). GPS was independently associated with OS (1.72, 1.05–2.82, p = 0.032) but not PFS (1.32, 0.88–1.98, p = 0.187). LAR-based models had lower Akaike information criterion values (ΔAIC 12.3 and 10.9), but concordance did not differ significantly between the indices (ΔC ≈ 0.04, p > 0.20). Conclusions: Baseline LAR, an inexpensive routine index, was associated with both endpoints, whereas GPS was associated with overall survival alone. Discrimination was modest for both indices (C-index ≤ 0.61) and did not differ significantly between them. External validation is required.