Exploratory Integrated Clinical Score and ICF-Defined Functioning in Non-Small Cell Lung Cancer: A Cross-Sectional Study

Background/Objectives: Spirometry is essential for respiratory assessment but does not fully characterize disability or everyday functioning. This study examined whether an exploratory Integrated Clinical Score (ICS), combining spirometric impairment and systemic inflammation, was associated with selected International Classification of Functioning, Disability and Health (ICF) categories in patients with non-small cell lung cancer (NSCLC) entering pulmonary rehabilitation. Methods: This cross-sectional baseline analysis included 62 consecutively recruited adults with histologically confirmed NSCLC. The ICS combined standardized FEV1, FVC, FEV1/FVC, and natural-log-transformed neutrophil-to-lymphocyte and platelet-to-lymphocyte ratios; higher values indicated greater disease burden. Eleven prespecified ICF categories were rated; eight categories formed the primary analysis set, while three Environmental Factors categories were analysed separately as exploratory. Associations were examined using Spearman correlations with Benjamini–Hochberg correction and proportional-odds models adjusted for age, sex, body mass index, and smoking status. Results: Higher ICS values were associated with greater difficulty in energy and drive functions, exercise tolerance, walking, daily routine, housework, and recreation and leisure (ρ = 0.34–0.39; all adjusted p < 0.05). Emotional functions were not associated with the ICS; pain reached significance only in the adjusted model (OR 1.61, 95% CI 1.02–2.55). Separate component analyses indicated that these associations were predominantly driven by the lung-function subscore, whereas the inflammation subscore was not significantly associated with any primary ICF category after correction for multiple testing. A 1-SD increase in the ICS was associated with a 0.37-point increase in the summary functional-difficulty index (95% CI 0.13–0.61; p = 0.003). Conclusions: The exploratory ICS was associated with functioning across several ICF domains, but these associations were predominantly driven by its lung-function component, and incremental value from adding inflammatory markers was not demonstrated. The ICS should therefore be regarded as a hypothesis-generating research construct rather than a validated clinical instrument; further studies should assess its reproducibility and incremental value beyond lung function alone.