**Background:** Renal cell cancer (RCC) accounts for >90% of kidney cancers, with 70–80% of patients diagnosed at localized stages (I–III). Despite curative treatment (partial or radical nephrectomy), 20–30% of patients experience relapse or progression. Classical prognostic factors (TNM stage, grade, histology) lack sufficient predictive accuracy. Over 60% of RCC patients are overweight or obese at diagnosis, yet a paradoxical association exists: higher BMI is linked to increased RCC risk but better survival. Body composition (visceral adipose tissue, skeletal muscle mass and density) may explain this paradox, but data in localized RCC are limited. The ReLife study aims to clarify associations of patient/tumor characteristics, lifestyle habits, and circulating biomarkers with body composition and clinical outcomes.
**Methods:** The ReLife study is a multicentre prospective cohort conducted across 18 hospitals in the East, South, and Central Netherlands. Eligible participants were men and women aged 18–75 years with newly diagnosed, histologically confirmed primary stages I–III RCC who underwent nephrectomy or ablation. Exclusion criteria included prior cancer within 5 years, lymph node or distant metastasis, and insufficient Dutch language proficiency. Recruitment ran from January 2018 to June 2021 (paused March–May 2020 due to COVID-19). Of 882 invited patients, 836 were eligible and 368 consented (response rate 44%). Data are collected at three time points: 3 months, 1 year, and 2 years after treatment. At each time point, participants complete questionnaires (demographics, lifestyle, diet via 163-item FFQ, physical activity via SQUASH, HRQoL via EORTC QLQ-C30), wear an activPAL accelerometer for 7 days, and provide blood samples (EDTA plasma, serum; DNA at 3 months only). Diagnostic and follow-up CT scans are collected for body composition analysis at L3 (skeletal muscle, VAT, SAT, IMAT areas and radiodensity). Clinical data (disease characteristics, treatment, complications, recurrence, progression, survival) are obtained from the Netherlands Cancer Registry. Power calculation: with 368 patients and an assumed 276 analyzable CT scans, the study has ≥80% power to detect a multiple correlation coefficient of 0.30 (Cohen's f²=0.10) for associations with body composition features, using Bonferroni correction (α=0.05/3).
**Key Results:** The cohort has a mean age of 62.4±9.0 years; 70% are male; 97% are White. Most patients have stage I disease (65%), Fuhrman grade 2 (50%), and were treated with radical nephrectomy (57%). Mean BMI is 27.6±4.7 kg/m²; 44% are overweight and 25% obese. Smoking history: 12% current, 50% former, 37% never. Alcohol consumption: 28% none, 39% >0–10 g/day, 27% >10 g/day. Moderate-to-vigorous physical activity: 52% ≥150 min/week, 39% 75–150 min/week, 7% <75 min/week. Comorbidities: 61% have ≥2 comorbidities. Compared with non-participants (n=468), participants were less likely to be male (70% vs. 77%, p=0.02) but similar in age, tumor stage, grade, morphology, and treatment. Data collection at 3 months and 1 year is finalized; 2-year follow-up is expected to be completed by June 2023.
**Clinical Implications:** The ReLife study is the first population-based prospective longitudinal study to comprehensively examine lifestyle factors, body composition, and clinical outcomes in localized RCC. By integrating questionnaire data, objective accelerometry, CT-derived body composition, blood biomarkers, and tumor tissue, it will generate evidence to develop personalized lifestyle advice for patients. Findings may clarify the obesity paradox in RCC, identify modifiable risk factors for poor outcomes, and improve risk stratification beyond traditional prognostic factors. Limitations include potential selection bias (44% response rate), possible attrition, lack of RCC-specific HRQoL measures, and limited power for survival analyses, which may require future data pooling.