Validation of disability status, a claims-based measure of functional status for cancer treatment and outcomes studies.

BACKGROUND: In prior research, we developed a claims-based prediction model for poor patient disability status (DS), a proxy measure for performance status, commonly used by oncologists to summarize patient functional status and assess ability of a patient to tolerate aggressive treatment. In this study, we implemented and validated the DS measure in 4 cohorts of cancer patients: early and advanced non-small cell lung cancers (NSCLC), stage IV estrogen receptor-negative (ER-) breast cancer, and myelodysplastic syndromes (MDS). DATA AND METHODS: SEER-Medicare data (1999-2007) for the 4 cohorts of cancer patients. Bivariate and multivariate logistic regression tested the association of the DS measure with designated cancer-directed treatments: early NSCLC (surgery), advanced NSCLC (chemotherapy), stage IV ER- breast cancer (chemotherapy), and MDS (erythropoiesis-stimulating agents). Treatment model fit was compared across model iterations.
RESULTS: In both unadjusted and adjusted results, predicted poor DS was strongly associated with a lower likelihood of cancer treatment receipt in all 4 cohorts [early NSCLC (N=20,280), advanced NSCLC (N=31,341), stage IV ER- breast cancer (N=1519), and MDS (N=6058)] independent of other patient, contextual, and disease characteristics, as well as the Charlson Comorbidity Index. Inclusion of the DS measure into models already controlling for other variables did not significantly improve model fit across the cohorts.
CONCLUSIONS: The DS measure is a significant independent predictor of cancer-directed treatment. Small changes in model fit associated with both DS and the Charlson Comorbidity Index suggest that unobserved factors continue to play a role in determining cancer treatments.