Table 2.

Heterogeneity in disease scenario simulation input parameters and resulting association between obesity and mortality, illustrated for renal cancer patients

Normal weightOverweightObesity
Input parameters
 Prevalence of weight status in the populationa0.3330.3330.333
 Lifetime indolent cancer riskb0.0100.0160.018
 Lifetime aggressive cancer riskb0.0010.0010.001
 Effect of weight status on indolent cancer incidencecRefOR = 1.50OR = 2.00
 Effect of weight status on aggressive cancer incidencecRefOR = 1.00OR = 1.00
Causal compared with resulting association between weight status and mortality among renal cancer patients
 Causal OR for weight status and mortality among cancer patientsdRefOR = 1.10OR = 1.30
 Resulting OR for weight status and mortality among cancer patientsRefOR = 0.94OR = 1.00
  • NOTE: We assumed 5-year survival among cancer-free adults of 0.93 (based on U.S. life tables for 65-year-olds; ref. 15) and 5-year survival of 0.80 among patients with indolent cancer type and 0.08 among patients with aggressive cancer type [based on SEER estimate of 5-year survival for renal cancer (all stages; ref. 16) and American Cancer Society survival estimates for renal cancer by stage (20)]. Results based on 1,000 replications.

  • aEstimate of effects of weight status on renal cancer incidence from a large U.S. cohort (17). Conceptually, our simulations assume that each individual's weight status is stable throughout the period they are at risk for developing renal cancer.

  • bEstimated based on SEER report of lifetime risk of kidney and renal pelvic cancers (0.016; ref. 16), and assuming 9% of renal cancer cases are an “aggressive” type and 91% are a relatively “indolent” type. As a proxy to estimate frequency of aggressive cancer type, we used stage 4 at diagnosis from Hakimi et al. (21).

  • cWe assumed that weight status has no effect on aggressive cancer incidence and that the effect of weight status on indolent cancer incidence is approximated by the effect of weight status on renal cancer overall because the vast majority of renal cancer is assumed to be of the indolent form.

  • dThe causal OR for weight status and mortality among cancer patients assumes that the true causal OR for weight status on mortality is the same in cancer patients as in the general population of U.S. adults. (ORs of 1.10 and 1.30 for overweight and obesity respectively; ref. 19).