Christian P. Pavlovich

Background To validate the use of a cumulative cancer locations (CCLO) score, a measurement of tumor volume on biopsy, and to develop a novel magnetic resonance imaging (MRI)‐informed CCLO (mCCLO) score to predict clinical outcomes on active surveillance (AS). Methods The CCLO score is a sum of uniquely involved sextants with prostate cancer on diagnostic + confirmatory biopsy. The mCCLO score incorporates MRI findings into the CCLO score. Participants included 1284 individuals enrolled on AS between 1994 and 2022, 343 of whom underwent prostate MRI. The primary outcome was grade reclassification (GR) to grade group ≥2 disease; the secondary outcome was receipt of definitive treatment. Results Increasing CCLO and mCCLO risk groups were associated with higher risk of GR and undergoing definitive treatment (both p < 0.001). On multivariable analysis, increasing mCCLO score was associated with higher risk of GR and receipt of definitive treatment (hazard ratios [HRs] per 1‐unit increase: 1.26 [95% confidence interval [CI]: 1.12–1.41] and 1.21 [95% CI: 1.07–1.36], respectively). The model using mCCLO score to predict GR (c‐index: 0.671; 95% CI: 0.621–0.721) performed at least as well as models using the number of cores positive for cancer (0.664 [0.613–0.715]; p = 0.7) and the maximum percentage of cancer in a core (0.641 [0.585–0.696]; p = 0.14). Conclusions The CCLO score is a valid, objective metric to predict GR and receipt of treatment in a large AS cohort. The ability of the MRI‐informed mCCLO to predict GR is on par with traditional metrics of tumor volume but is more descriptive and may benefit from greater reproducibility. The mCCLO score can be implemented as a shorthand, informative tool for counseling patients about whether to remain on AS.