Patient selection for prostate focal therapy in the era of active surveillance: an International Delphi Consensus Project

Abstract

Whole-gland treatment of the prostate gland, either by extirpation or irradiation is considered the gold standard for curative oncological treatment of men with localized prostate cancer.1, 2 However, after cure, many men live with sexual and urinary impairment that adversely affects their quality of life.3 This has led to increased interest in developing therapies with effective cancer control, but less morbidity. Localized prostate cancer has a long natural history and cancer-specific mortality is more likely in men with higher-grade disease.4, 5 Two of the longest running active surveillance (AS) trials have also shown that men with low-grade cancer have an indolent course at 10-15 years of follow-up.6, 7 Detailed examination of one of the cohorts with a broader inclusion criteria showed that the majority of men who developed metastasis while on observation had intermediate grade (Gleason 3+4) cancer.8 Indeed, Gleason grade 4 harbors many more molecular hallmarks of cancer compared to Gleason grade 3.9 Advances in imaging and targeted biopsy have improved the ability to differentiate intermediate- and high-grade cancers from indolent ones. In the past, where transrectal ultrasound-guided (TRUS) biopsy was deemed inadequate, trans-perineal template mapping biopsies were used to map cancers for targeted treatment. These require a large number of samples, tend to over-detect low-grade cancers, and can be associated with additional costs and complications.10, 11 Multiparametric magnetic resonance imaging (mpMRI) improves staging and preferentially detects higher-grade cancers, whereas MRI–TRUS fusion systems now allow physicians to target suspicious areas accurately.12, 13, 14, 15 The ability to better determine cancer grade and extent has led to a renewed interest in partial gland ablation treatments such as focal therapy (FT), whereby only the area of the prostate harboring clinically significant disease is treated, sparing collateral structures and resulting in less morbidity than a whole-gland approach. FT would be an ideal approach for localized small-volume cancers of intermediate or high grade if they could be accurately targeted and treated completely, leaving areas of indolent cancer that do not pose a biological threat to be actively monitored with AS.16 Conceptually, if detected early enough and treated effectively, this approach would alter the long-term risk of disease progression. The key to this approach is patient selection—this strategy has a greater likelihood of success when applied to an individual with a suitable disease burden. The rate of technological and biological advances has outpaced the ability to accrue meaningful data regarding the best patient selection criteria. Many early trials were performed in men with low-risk prostate cancer who would be on AS today and early efforts in patient selection focused mainly on predicting the presence of unilateral cancer for purposes of hemiablation rather than true focal ablation.17, 18 We aim to develop a contemporary expert consensus on patient selection for FT of prostate cancer in the era where intermediate-/high-grade cancer could be treated focally while low-grade cancers might be monitored. Of 219 identified articles, 36 were deemed suitable after critical appraisal of the full text (Figure 1). Issues identified were grouped into three domains for construction of the survey questionnaires: (1) role of mpMRI and biopsy, (2) disease factors and (3) patient factors. Of 113 experts identified, 51 responded to the first round of online survey. For the second and third online rounds, the response rate was 92.1% (47 experts in each round). Participant demographics are detailed in Figure 2. In the fourth round, 16 experts, all of whom had completed three online rounds, formed a core group to interpret the findings of the online rounds. We arrived at consensus in 16/18 subdomains of the three main domains. These are summarized in Table 1. In addition, areas where consensus was not reached and represent controversy in patient selection for FT today are summarized in Table 2. The panel agreed that in MRI-negative areas, systematic biopsies remain necessary even if an MRI suspicious lesion has already been sampled adequately in a targeted manner (90%). There was also strong agreement on this within the core group, with only one member feeling certain that this modus operandi would change in the near future due to improved performance of mpMRI. However, while there was consensus that 80% of experts would treat a 3+3 lesion up to 2 ml, 67% would treat 3+3 up to 5 ml, >80% would treat 3+4 up to 2 ml, 52% would treat 3+4 up to 5 ml and 80% would treat 4+3 up to 0.5 ml. No consensus was reached on tumors of any size with a Gleason score4+4. In the untreated zone outside of where FT was planned, the panel agreed that untreated Gleason 3+3 cancer is acceptable though there was no clear agreement on disease burden thresholds: 46% of experts would accept up to three cores of cancer, whereas 96% would accept up to one core 1 mm of cancer. The panel agreed that untreated Gleason 4+3 cancer is unacceptable at any disease burden (87%). The panel agreed that the potential for preservation of erectile function is an important reason for choosing FT over radical treatment (93%). However, there was no agreement on a meaningful International Index for Erectile Function threshold, below which it would not be worth pursuing FT. Furthermore, the panel consensus indicates that lack of erectile function at baseline should not exclude a patient from FT: 83% of experts would not choose whole-gland ablation over FT and 72% would not choose prostatectomy/radiation over FT in a fit, young man who is impotent but has a lesion amenable to FT. The majority of early FT trials primarily included low-risk prostate cancer patients who would today be considered suitable for AS. In the 2009 consensus meeting by de la Rosette et al.,21 the stated...