Abstract Background: Immunotherapy has transformed melanoma treatment, but its promise is not equitably distributed. Biomarker disparities-particularly in tumor-infiltrating lymphocyte (TIL) classification may limit access to precision treatment among patients from low-resource settings. Visual histopathologic scoring of TILs into brisk, non-brisk, or absent categories remains standard practice, but this subjective method is prone to interobserver variability and lacks standardization. This is especially problematic in underrepresented African populations, where diagnostic tools and molecular profiling resources are limited. We aimed to validate conventional TIL classification using cytokine-based immune scoring and explore its implications for biomarker equity in melanoma care. Methods: A total of 205 formalin-fixed, paraffin-embedded (FFPE) primary cutaneous melanoma samples from South African patients were categorized histologically based on AACR-defined TIL criteria. Immunohistochemical (IHC) staining for tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ) was performed using an automated platform. Cytokine expression was quantified using a modified Allred scoring system, which combines staining intensity and proportion of positive cells. Concordance between histologic TIL classification and cytokine-based immune scores was assessed through positive predictive value (PPV) and negative predictive value (NPV) analysis. Results: In the brisk TIL group, TNF-α and IFN-γ immune scores showed PPVs of 0.68 and 0.79, respectively, suggesting moderate to strong correlation between histologic appearance and cytokine activation. In the absent TIL group, NPVs were 0.84 (TNF-α) and 0.91 (IFN-γ), indicating reliable association with immunologically quiescent tumors. However, a subset of histologically “TIL-absent” tumors demonstrated strong cytokine expression, highlighting biologic heterogeneity and potential misclassification. These discordances have real-world implications, especially where visual interpretation is the only method available to guide treatment. Conclusion: Our findings underscore the value of cytokine-based immune scoring in validating and standardizing TIL classification. In underserved settings, where access to advanced genomic assays is limited, incorporating affordable and accessible IHC-based immune profiling may improve diagnostic accuracy and expand equitable access to immunotherapy. As immunotherapy eligibility increasingly depends on biomarker evidence, such approaches are essential to closing gaps in precision oncology and addressing global cancer care disparities. Citation Format: Meshack Bida, Rodney Hull, Thabiso Miya, Tebogo Marutha, Zodwa Dlamini. Validating tumor-infiltrating lymphocyte classification in primary cutaneous melanoma using cytokine immune scores: Addressing biomarker disparities in underserved populations abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6465.
Bida et al. (Fri,) studied this question.