Prognostic utility of the CALLY index in metastatic melanoma: building a nomogram for Patients on Anti-PD-1 therapy

BACKGROUND: Despite the success of immune checkpoint inhibitors (ICIs) in metastatic melanoma, many patients fail to derive meaningful benefit, underscoring the urgent need for accessible prognostic biomarkers. The C-reactive protein (CRP)-albumin-lymphocyte (CALLY) index, an immunonutritional index, has shown prognostic value in various cancers. Previous studies indicate that systemic inflammation and nutritional status influence ICI efficacy, suggesting the potential relevance of the CALLY index in metastatic melanoma. This study evaluates the CALLY index's role in metastatic melanoma patients treated with anti-PD-1 therapy. METHODS: This retrospective study analysed 92 patients with metastatic melanoma who were treated with anti-PD-1 monotherapy at Ege University's Faculty of Medicine between 2015 and 2023. The CALLY index was calculated using the pre-treatment CRP, albumin and lymphocyte levels. Kaplan-Meier analysis was used to estimate survival outcomes, and univariate and multivariate Cox regression models were employed to identify independent prognostic factors. A predictive nomogram incorporating the CALLY index and other significant variables was then developed. RESULTS: The optimal CALLY index cutoff was determined to be 2. Patients with a low CALLY index (≤ 2) had worse median overall survival (OS) and progression-free survival (PFS) when compared with those who had a high CALLY index (> 2) (median OS: 9.6 vs 31.3 months, p < 0.001; median PFS: 3.8 vs 10.6 months, p = 0.001). Multivariate analysis identified the CALLY index, lactate dehydrogenase above the upper limit of normal, Eastern Cooperative Oncology Group score ≥ 2, M1c/M1d staging and acral/mucosal melanoma subtypes to be independent predictors of OS. A nomogram was then constructed based on these factors, yielding a concordance index of 0.705 (95% confidence interval: 0.634-0.776). This model stratified patients into low-, intermediate- and high-risk groups, with the high-risk group showing significantly worse OS than the intermediate- and the low-risk groups (p < 0.001). CONCLUSION: The CALLY index is a cost-effective and independent prognostic biomarker that can aid in risk stratification and guide treatment decisions in patients with metastatic melanoma receiving anti-PD-1 therapy.