Discordance between G8 and functional competence and their associations with quality of life in urological cancers

G8 and functional competence may capture different aspects of vulnerability in patients with cancer, but their relationship and associations with quality of life remain unclear. We evaluated the concordance between G8 and functional competence and their associations with health-related quality of life (HRQOL) in patients with urological cancers. We retrospectively analyzed prospectively collected observational data from 1,955 patients with renal cell carcinoma, urothelial carcinoma, or prostate cancer. Functional competence was assessed using the 13-item Tokyo Metropolitan Institute of Gerontology Index of Competence (TMIG-IC), and HRQOL was available for 1,580 patients. Associations between G8 and TMIG-IC were assessed using Spearman’s rank correlation and Cohen’s κ. G8 ≤ 14 and TMIG-IC < 11 were used as abnormal criteria. Poor global quality of life (QOL) was defined as an EORTC QLQ-C30 global QOL score ≤50. G8 and TMIG-IC showed weak correlation (rₛ = 0.361) and low concordance (κ = 0.204). G8 ≤ 14 and TMIG-IC < 11 were independently associated with poor global QOL (odds ratios 2.74 and 2.55, respectively; both p < 0.001). After additional adjustment for the G8 self-rated health item, both associations remained significant. Poor global QOL increased stepwise among patients meeting neither, one, or both criteria (16.9%, 37.7%, and 65.2%, respectively). The findings were similar in patients aged ≥65 years. Both measures were also associated with overall survival in an exploratory analysis of metastatic disease. G8 and TMIG-IC showed limited concordance but were independently associated with poor global QOL. Their combined assessment may provide complementary information on patient vulnerability.