Der Body mass index als Prognosefaktor bei Patienten mit Nierenzellkarzinom nach radikaler Primärtumorresektion

Renal cell cancer represents the tumor with the highest mortality among urological malignancies. Due to its increasing incidence over the last decades there is a special need for the establishment of additional prognostic criteria to define high risk patients. In the present retrospective monocentric study the influence of the Body Mass Index (BMI) was analysed on the prognosis of patients with renal cell carcinoma after radical tumor resection. All patients (n=771 evaluable) had been treated in the Department of Urology, University of Marburg, between 1990 and 2005. The analysis focused on both BMI classifications, a) BMI groups according to the WHO definition (2000) and b) after age adjustment. Using Kaplan-Meier analysis, a statistically significant difference in cancer specific survival was observed between the five WHO-BMI groups (p=0,014) with the highest 5-years survival of 92% in obese patients (obesity grade II and III, i.e. BMI > 35 kg/m2). In addition, in this group significantly fewer patients died from renal cell cancer in comparison to patient with normal- or overweight (p=0,035). However, applying multivariate analysis including tumour grade, stage, lymphatic metastasis , and pulmonary / visceral metastasis, BMI-groups according to the WHO-classification could not be retained as a significant independent prognostic marker (p=0.096, cox regression analysis). In a further analysis, combined BMI groups with a cut off at 25 kg/m2 showed a statistically significant difference in cancer specific survival using Kaplan-Meier analysis (p=0,003) with 5-years survival of 80% for BMI greater 25 kg/m2 and 72% for BMI lower 25 kg/m2. Applying multivariate analysis this subgroup analysis (BMI greater 25 kg/m2 versus lower 25 kg/m2) retained overweight/obesity as an independent prognostic criteria (p=0.004, cox regression analysis). After adjusting BMI-groups according to the patients age, univariat analysis revealed a significantly better tumor specific survival in overweight patients in comparison to those with under- and normal weight (p=0,039). In addition to the results for the combined BMI-groups according to the WHO-classification, in our patient collective the age adjusted BMI-classification could also be confirmed as an independent prognostic factor using multivariate analysis (p=0.04, cox regression model). No correlation was found between BMI and histological subtype, tumor stage, tumor-grade, lymph node involvement or distant metastasis, neither in BMI subgroups according to WHO nor BMI-groups classified after age adjustment. In conclusion, these results confirm and extend previous findings that in patients suffering from renal cell carcinoma overweight/obesity is associated with a better prognosis.