Comorbidity in newly diagnosed thyroid cancer patients: a population-based study on prevalence and the impact on treatment and survival

BACKGROUND: Comorbidity may be an important contributory factor to differences in the treatment and outcome of cancer, especially in older patients. It might also provide information on the aetiology of the cancer in cases of high or low frequency. The aim of this study was to describe the spectrum of comorbidity and the possible impact on treatment and survival in newly diagnosed thyroid cancer (TC). DESIGN: A population-based observational study. SETTING: The Eindhoven Cancer Registry, Comprehensive Cancer Centre South (IKZ), the Netherlands. METHODS: Demographic, histological and treatment data on all 417 TC patients diagnosed between 1 January 1993 and 31 December 2002 were collected and followed up till 2004. An adapted version of the list of Charlson was used for registration of clinically relevant concomitant disorders. The prevalence of comorbidity at diagnosis was analysed according to gender, age, histological type and therapy. Crude 6-month and 1- and 5-year survival rates were determined. A regression analysis was performed to identify independent variables related to survival. RESULTS: Information on comorbidity was available for 378 patients (91%). Comorbidity was present in 32% of the patients; 23% had one and 12% had two or more concomitant diseases. The prevalence of comorbidity increased with age. Hypertension was the most frequent comorbidity (18%), followed by 'other cancers' (7%), cardiovascular diseases (6%) and diabetes mellitus (6%). The prevalence of hypertension was twice as high as expected at all age groups. Six patients > 60 years had had tuberculosis. Initial surgical treatment was negatively related to the presence of concomitant diseases in patients < 70 years (P = 0.02), but not in patients > or = 70 years. Comorbidity was not independently associated with crude survival up to 5 years. CONCLUSIONS: A previous diagnosis of hypertension was associated with TC. The use of external radiation for diagnostic and therapeutic procedures for tuberculosis probably explains the high prevalence of former tuberculosis in elderly TC patients. Treatment choices appeared to be influenced by the presence of comorbidity. Comorbidity did not affect survival up to 5 years; a study with a longer period of follow-up is needed.