Prostate cancer is one of the most common cancers in men in the United States, as well as a leading source of morbidity and mortality.¹ With the advent of MRI and targeted biopsy, it has become feasible to identify patients with clinically significant prostate cancer who are candidates for image-guided partial gland ablation. Partial gland ablation aims to achieve adequate cancer control while avoiding many of the adverse functional outcomes commonly associated with whole-gland treatment of prostate cancer, such as erectile dysfunction and urinary incontinence.² Although partial gland ablation has become an increasingly accepted practice in recent years, there is no consensus on protocols for monitoring oncologic outcomes after ablation and no agreed-upon indications for postablation biopsy.

There are many available energy sources for partial gland ablation; our institution primarily uses cryoablation since it has been shown to reliably achieve confluence of energy in the ablated zone.³ Oncologic outcomes after partial gland cryoablation are poorly defined, with existing studies limited to single-center retrospective cohorts where patients underwent postcryoablation surveillance without rigorous disease monitoring/biopsy protocols.^4-7 Since March 2017, men undergoing primary prostate gland cryoablation at our large urban medical center have been enrolled in a prospective outcomes registry with a protocol mandating uniform timing of oncological monitoring with PSA, multiparametric MRI (mpMRI), and biopsy. Initially, we required all men to undergo PSA testing at 3 and 6 months following cryoablation and every 6 months subsequently, mpMRI at 6 months, 3.5 years, and 5 years following cryoablation, and prostate biopsy at 6 months, 2 years, and 5 years following cryoablation. Additionally, men with suspicion for recurrence were required to undergo mpMRI and biopsy outside the mandated schedule at provider discretion. After an analysis of our outcomes in 2020 which showed very low rates of recurrence of clinically significant prostate cancer within the first 6 months after cryoablation, we stopped requiring biopsy at 6 months postcryoablation.³

Given that oncologic outcomes following prostate gland ablation are dependent on baseline characteristics of disease, the present study was limited to men with a Prostate Imaging Reporting & Data System 2-5 lesion concordant with unilateral intermediate risk disease (Gleason Grade Group [GGG] 2 or 3). Those with contralateral GGG >1 or any distal apical disease or gross extraprostatic extension on mpMRI were excluded from the study. Additionally, only those with at least 24 months of follow-up data were included for analysis. Recurrence of clinically significant prostate cancer was defined as GGG >1 disease on biopsy and was assessed separately for in-field, out-of-field, and overall recurrences. Failure of treatment was defined as receipt of whole-gland salvage treatment, metastatic prostate cancer, or prostate cancer mortality. Patients who underwent biopsy between 18 and 36 months postcryoablation were adherent to the surveillance protocol, as were those who recurred prior to eligibility for biopsy 2 years postcryoablation. Patients who had not undergone biopsy by 36 months postcryoablation were considered nonadherent with the surveillance protocol. Since patients could only be determined to recur in the present study through biopsy, the exact moment of recurrence was not possible to define, such that our survival data were treated as interval-censored in our analyses (with the exception of receipt of whole-gland salvage treatment and death of prostate cancer–related causes, which were not interval-censored). Nonparametric maximum likelihood estimators were calculated to model freedom from recurrence of clinically significant prostate cancer in-field, out-of-field, and overall, as well as freedom from failure of treatment. Ninety-five percent confidence intervals for these estimators at 36 months postcryoablation were estimated using 1,000 bootstrap replications. Analyses were conducted using R and package interval (version 1.1-0.8).

One hundred thirty-two men were included in the study, of whom 24 (18%) did not adhere to the surveillance protocol (Figure 1). Twelve of these men recurred with clinically significant prostate cancer, of whom 4, 4, and 2 were managed with active surveillance, salvage cryoablation, and salvage radical prostatectomy. Two men were recommended whole-gland salvage treatment but refused treatment. Model-predicted probabilities of 36-month postcryoablation freedom from recurrence of in-field, out-of-field, and overall clinically significant prostate cancer were 97% (95% CI: 92-100), 87% (95% CI: 80-94), and 86% (95% CI: 78-93), respectively (Figure 2). The model-predicted probability of freedom from failure of treatment at 36 months postcryoablation was 97% (95% CI: 93-100).

Based on the low rate of recurrence of clinically significant prostate cancer within 36 months after partial gland cryoablation, we no longer routinely perform surveillance biopsy at 2 years for men with intermediate-risk unilateral disease at baseline. We now reserve biopsy within the first 2 years postcryoablation for men with concern for recurrence, such as rising PSA levels, new regions of interest on mpMRI, or concerning digital rectal examination. All men in our prospective outcomes registry are now being encouraged to undergo mpMRI at 3.5 and 5 years, as well as biopsy at 5 years, to further improve our understanding of the intermediate oncologic outcomes of primary partial gland cryoablation.