Evaluation of comorbidity in 9388 head and neck cancer patients: a national cohort study from the DAHANCA database.

BACKGROUND: Comorbidity is common in head and neck squamous cell carcinoma (HNSCC) patients due to the etiology of the disease being primarily smoking. The aim of this study was to investigate the impact of comorbidity on survival in a national population-based cohort study on 9388 HNSCC-patients treated with radiotherapy (RT), to re-evaluate the prognostic impact of individual diseases within the Charlson Comorbidity Index (CCI), and to develop a revised head and neck comorbidity index (HN-CCI). MATERIAL AND METHODS: A national cohort of 9388 HNSCC-patients treated with curative intended RT diagnosed from 1992 to 2008 was identified from the DAHANCA-database. Data on comorbidity prior to HNSCC-diagnosis was obtained from the National Patient Registry and adapted to the CCI. RESULTS: By dividing the patients into two groups, we tested and validated which type of comorbidities within the CCI affected overall survival (OS) and cancer specific death (CSD). In total, 36% of patients had comorbidity. Six comorbid conditions within the CCI significantly reduced five-year OS probability: congestive heart failure, cerebrovascular disease, chronic pulmonary disease, peptic ulcer disease, liver disease, and diabetes, and based on these conditions the new head and neck specific comorbidity index was developed, the HN-CCI. Comorbidity according to HN-CCI had a highly significant impact on OS, whereas it was not associated with CSD. Chronological age was not associated with increased risk of CSD after controlling for comorbidity. CONCLUSIONS: Comorbidity is frequent in HNSCC patients and negatively impacts OS. Therefore assessment of comorbidity will be of great importance, both in order to treat/optimize patient's health before radiotherapy, but also in order to be able to stratify/control for comorbidity in randomized trials to avoid bias. Re-evaluation of the CCI revealed that only six conditions had an impact on survival, and a new modified index to assess comorbidity for HNSCC-patients was developed. The performance of HN-CCI to stratify patients on survival was good and HN-CCI is highly recommended for future assessment of comorbidity and prognostic staging of radiotherapy-treated HNSCC-patients.