A novel predictor of clinical progression in patients on active surveillance for prostate cancer

Validating the total cancer location density metric for stratifying patients with low-risk localized prostate cancer at higher risk of grade group reclassification while on active surveillance

PURPOSE

To validate a previously proposed prognostic metric, Total Cancer Location (TCLo) density, in a contemporary cohort of men with grade group (GG) 1 prostate cancer (PCa) on active surveillance (AS).

METHODS

We evaluated 123 patients who entered AS with maximum GG1 PCa at diagnostic and/or confirmatory biopsy. TCLo was defined as the total number of PCa locations identified on both biopsy sessions. TCLo density was calculated as TCLo / prostate volume [ml]. Primary endpoint was progression-free survival (PFS), defined as time from confirmatory biopsy to grade group reclassification (GGR) on repeat biopsy or prostatectomy. Optimal cut-point for TCLo density was predefined in a previously reported cohort and applied to this contemporary cohort. Kaplan-Meier and multivariable Cox regression analysis were used to estimate the association of predictors with PFS.

RESULTS

During median follow-up of 7.8 years, (IQR 7.3-8.2) 34 men had GGR. Using previously defined cut-points, PFS at 5-years was 60% (95% CI: 44%-81%) vs. 89% (95% CI: 83%-96%) in men with high (≥0.06 ml^-1) vs. low (<0.06 ml^-1) TCLo density, and 63% (95% CI: 48%-82%) vs. 90% (95% CI: 83%-96%) in men with high (≥3) vs. low (≤2) TCLo (log-rank test: P < 0.0001, respectively). Adjusting for age, prostate volume, percent of positive cores and PSA, both higher TCLo density (HR [per 0.01 ml^-1 increase]: 1.18, 95% CI: 1.05-1.33, P = 0.005) and TCLo (HR: 1.69, 95% CI: 1.20-2.38, P = 0.002) were associated with shorter PFS.

CONCLUSION

The previously suggested prognostic value of TCLo density was confirmed in this validation cohort. TCLo alone performed similarly well. Patients with high TCLo density (≥0.06 ml^-1) or TCLo (>2) were at greater risk of GGR while on AS. With external validation, these metric may help guide risk-adapted surveillance protocols.

Determining Clinically Based Factors Associated With Reclassification in the Pre-MRI Era using a Large Prospective Active Surveillance Cohort

OBJECTIVE

To report biopsy-related and oncologic outcomes in a large prospective active surveillance cohort that was initiated in the premagnetic resonance imaging era and to additionally identify clinical factors associated with disease reclassification in order to inform future studies designed to improve enrollment and follow-up on active surveillance.

METHODS

Patients were prospectively enrolled at a single institution from 2006 to 2014 and followed until 2016. Men with Gleason 6 or 7 disease were eligible, and those with >6 months follow-up were included in the analysis. Patients were risk stratified based on clinical/pathologic criteria, including based on a combination of baseline and confirmatory biopsy tumor characteristics. Reclassification-free survival, based on tumor volume increase or Gleason score increase, was analyzed using multivariable Cox proportional hazards models.

RESULTS

Of 825 enrolled patients, 682 met inclusion criteria. Median follow-up was 40 months (range 6.6-126.8). Disease was reclassified in 249 (36.5%), and 157 (23.0%) underwent treatment. A single positive core with a negative confirmatory biopsy was significantly associated with time to reclassification (median not met vs 43 months, log rank test P <.001). Composite tumor length, defined as the combined tumor length between baseline and confirmatory biopsies, was associated with shorter Gleason upgrade-free survival (hazard ratio 1.24, 95% confidence interval 1.11-1.40, P <.001) in multivariable analysis.

CONCLUSION

Baseline stratification using clinical factors including tumor length may refine risk stratification and offer the foundation on which new systems that incorporate modalities such as magnetic resonance imaging may be based.