Two-years Postradiotherapy Biopsies: Lessons from MRC RT01 Trial

Background The importance of 2-yr postradiotherapy prostate biopsy status remains uncertain. Objective To assess the value of 2 year post treatment biopsies in a randomised trial of radiotherapy dose escalation. Design, setting, and participants Between 1998 and 2001, 843 men with localised prostate cancer were randomised to receive either control-64 Gy or escalated-74 Gy conformal radiotherapy (CFRT) in the MRC RT01 trial in combination with 3–6-mo neoadjuvant androgen deprivation therapy. Prostate biopsies were planned at 2 yr from start of CFRT in suitable men. Outcome measurements and statistical analysis Prostate biopsy results and prostate-specific antigen (PSA) levels performed at 2 yr post-CFRT were evaluated with long-term biochemical progression free survival (bPFS) and overall survival. Outcome measures were timed from the 2-yr biopsy using a landmark approach. Results and limitations A 2-yr biopsy was performed in 312/843 patients. One hundred and seventy-seven patients were included in the per-protocol group with median follow-up of 7.8 yr from biopsy. Median PSA at biopsy was 0.5 ng/ml. Sixty-four bPFS events were reported: 46/145 (32%) in patients with negative, 6/18 (33%) suspicious, and 12/14 (86%) positive biopsies. A positive biopsy was prognostic of worse bPFS, going forward, compared with negative and suspicious biopsies, hazard ratio (HR) = 4.81 (95% confidence interval [CI]: 2.50–9.26, p < 0.001). The estimate for survival was HR = 1.58 (95% CI: 0.52–4.78, p = 0.42). PSA values at 2 yr between 1.01 ng/ml and 2.09 ng/ml were also associated with subsequent PSA failures (HR = 2.71, 95% CI: 1.98–3.71), bPFS events (HR = 2.45, 95% CI: 1.81–3.32), and prostate cancer-specific survival (HR = 2.87, 95% CI: 1.08–7.64) compared with PSA ≤1.0 ng/ml. Conclusions Two-year postradiotherapy prostate biopsies have limited value in patients with PSA control but both positive biopsy and higher PSA status are strongly associated with future bPFS events. A policy of selected biopsy may provide an opportunity for early salvage interventions. Patient summary Routine 2-yr postradiotherapy biopsy is not recommended but can be considered in selected patients with unfavourable post-treatment prostate-specific antigen levels who are suitable for early salvage treatments.


Introduction
There is controversy over the value of prostate biopsy after radiotherapy (RT) treatment for prostate cancer in predicting future survival and recurrence trends [1,2]. The inherent difficulties in interpreting postradiation prostate biopsies [3] and debate regarding the optimal time of performing those biopsies have contributed to the uncertainty [1,4].
Previous reports have suggested that men with a positive biopsy post-RT have a much worse prognosis than those with negative biopsies. However, most of these reports included a small number of patients, short-term follow-up, and heterogeneous methods of pathology reporting [5][6][7][8]. Our study included a large, prospectively-recruited cohort of patients participating in a randomised controlled trial, with 10-yr follow-up and a single reference pathologist.

2.
Materials and methods

Design of the RT01 trial and treatments
The design, objectives, patient eligibility criteria, treatment methods of the RT01 trial have been detailed previously [9][10][11]. In brief, consenting men with histologically confirmed T1b-T3a N0 M0 prostate cancer and prostate-specific antigen (PSA) levels <50 ng/ml were registered.
Patients having conformally-delivered radiotherapy were randomised to receive either a control schedule of 64 Gy/32f RT (Std-64 Gy) or an escalated schedule of 74 Gy/37f (Esc-74 Gy). Neo-adjuvant androgen deprivation therapy was administered 3-6 mo prior to RT and was maintained until the end of RT. Based on pathology grading, PSA, and T-stage, men were stratified into two groups according to the risk of seminal vesicles involvement (low or moderate/high risk) [12].
The trial followed the principles of the Declaration of Helsinki. Each centre attained ethical approval and participants gave separate informed consent for trial participation and the 2-yr biopsy.

Local histopathology review 2-yr biopsy group
This included patients without a prior bPFS event who had 2-yr biopsy which was reviewed locally (with or without central review). The same exclusion criteria applied as for the PPG. Analyses were timed from the 2yr biopsy.

Exploratory group
This included only patients with a bPFS event at or before the 2-yr biopsy.
Analyses were timed from randomisation.

Two-year PSA group
This included all patients with a PSA value within 20-28 mo after randomisation (whether biopsied or unbiopsied), who were bPFS-event- 3.

Results
Data were frozen on August 2, 2011, matching the previous results paper [10].

Patient populations
Of the 843 men randomised in RT01, 312 men (37%) underwent a 2-yr biopsy of the prostate. Median time from starting RT to biopsy was 2.1 yr (interquartile range: 2.0-2.2). Three hundred and eleven out of 312 (99.7%) biopsies were reviewed locally and 223/312 (71%) were reviewed centrally. Seventy out of 312 (22%) patients were excluded from the PPG, mainly (65/70) because a bPFS event was reported before or on the date of 2-yr biopsy (Fig. 1).
Notably, 2/14 (14%) patients with positive prostate biopsies at 2-yr had no evidence of bPFS or clinical failure after completing 10-yr follow-up. Two-year PSA levels were 0.1 ng/ml and 0.2 ng/ml.

Baseline characteristics
The median age, Gleason score, and SV involvement risk groups of the 311 LBG patients were similar to the main trial population (Supplementary Table 2).

All outcome measures: results
Survival and bPFS results in the LBG group are broadly consistent with the PPG (Supplementary Table 3, Fig. 1

Discussion
Failure to eradicate local tumours correlates with distant metastases development, cancer-related death, and overall survival [15,16] and presently, post-RT prostate biopsy remains the only direct measure of local tumour control [17]. In agreement with other studies [4,15,16,18,19], our results show that prostate biopsies performed between 18 mo and 36 mo after RT are highly prognostic of future biochemical failure and disease-free status at 10 yr. As reported in previous studies, we found similar prognostic value for indeterminate and negative biopsies for subsequent biochemical failure [15,17,18,20]. We recognise the low positive biopsy rate in our study [15,17]. In particular, the differences between our study and RTOG 9408 which reported a 30% positive biopsy rate are of interest [19]. Potential causes for our lower biopsy positive rate include the use of dose escalation in 50% of the patients who had a considerably lower rate of positive biopsies (74 Gy 4% vs 64 Gy 12%), the use of 6 mo rather than 4 mo androgen suppression and the strict exclusion of patients who had PSA failure at the 2-yr time point. In our EG who had PSA failure before or on the date of their 2-yr biopsy, 41% had positive biopsies. Finally, our study used two to four biopsies and a higher positive biopsy rate might have been found if more comprehensive prostate sampling had been employed particularly if using MRI guidance.
We previously reported that 39% (91/236) of deaths in the RT01 trial were due to prostate cancer [10] and PCSS is a more appropriate outcome measure for assessing the value of positive prostate biopsies than overall survival. We observed significantly poorer PCSS in patients with positive 2-yr biopsies with HR of 15.6 and 9.8 in the PPG and LPG groups, respectively; however, our evidence is limited due to the small number of deaths (4/27 in PPG group), which probably relates to case selection for biopsy excluding patients with early PSA failure. Nevertheless, the data is in accord with Zelefsky et al [15] who demonstrated a threefold increase in the rate of deaths from prostate cancer after 10-yr follow-up after a positive biopsy in intermediate-or high-risk prostate cancer patients treated with RT.
We noted that early biochemical failure correlates with a higher positive biopsy rate when compared with the general PPG; this could be attributed to early local recurrence reflecting more aggressive tumours. We also observed that biochemical failure does not always correlate Esc with positive biopsies as 27/46 (59%) of cases with biochemical failure in the EG had negative biopsies. This is probably due to the development of extra-prostatic recurrence as the cause of PSA failure or, alternatively missing the recurrent focus of tumour during biopsy, yielding false-negative results.
PSA values at 2 yr were significantly correlated with biopsy outcomes, bPFS, PCSS, with PSA >1 ng/ml associated with a 2.7 higher chance of future biochemical failure than PSA 1 ng/ml. This is in agreement with previous studies reporting the importance of PSA nadir in predicting biochemical failure and disease-free survival [21][22][23][24].
[ ( F i g . _ 2 ) T D $ F I G ]     Prostate biopsy has disadvantages; it is an invasive procedure with risk of infection and bleeding. The uptake of biopsies in this study was modest with only 37% compliance. However, this is quite similar to the RTOG 9408 study where 42% of patients were biopsied [19] suggesting that this is the realistic proportion of patients who are likely to be suitable and consent to biopsy in such large multi-centre randomised trials. The timing of post-treatment biopsies is problematic and false-positive results occur. Crook et al [4] demonstrated that 30% of initially indeterminate biopsies at 13 mo cleared at a mean time of 31.6 mo; this is thought to be secondary to the prolonged killing effect of RT. In this series, two patients had positive biopsies at 2 yr with no evidence of biochemical recurrence 10 yr following RT. Conversely, sampling errors may lead to potential falsenegative results.
Pathology interpretation is not straightforward and different assessment methods have been proposed [16,21]. In this series, 27% (11/40) of biopsies scored positive by local pathologists were downgraded to indeterminate or negative.
Since this study multiparametric MRI (mpMRI) of the prostate has become an increasingly reliable method to diagnose loco-regional and distant recurrence combining T2 with diffusion weighted imaging [25,26]. One recent study comparing mpMRI with histopathology after salvage prostatectomy post-RT showed 50-71% sensitivity with 80-100% specificity for detecting extra-prostatic extension [27]. A further study reported an area under the curve of 0.84 when using mpMRI to detect local recurrence compared with template transperineal biopsies [28]. Early results assessing prostate-specific membrane antigenpositron emission tomography appear promising [29].
Despite the association of positive post-RT prostate biopsies with future bPFS and CSS, we would not recommend routine biopsy in line with current practice in the UK. Biopsy remains essential in selected patients led by unfavourable post-treatment PSA profiles combined with MRI in patients suitable and favouring local salvage treatment. Clarification of the role of imaging and biopsy in patients with post-treatment PSA levels 1.0-2.0 ng/ml would be of value. For both the poor prognostic group of patients with PSA failure before 2 yr and an intermediate group with PSA levels 1-2 ng/ml at 2 yr imaging reassessment might be considered. Prostate biopsy would only be indicated after exclusion of extra-pelvic disease and there should be MRI or other imaging evidence of locally persistent disease. The patient must be suitable for and want local salvage treatment. For the good prognosis group of patients with PSA level of 1 ng/ml, the recurrence rate is low with excellent long-term outcomes and we would not recommend biopsy.

Conclusions
Prostate biopsies performed 2 yr after radical RT using contemporary doses with neoadjuvant androgen deprivation therapy are rarely positive in patients with PSA 2 ng/ ml but are associated with poor outcome. PSA failure within 2 yr of RT identifies a population at high risk of death from prostate cancer. PSA-led prostate biopsies post-treatment should be considered in selected patients suitable for local salvage procedures.
Author contributions: David Dearnaley had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Administrative, technical, or material support: Murphy.
Financial disclosures: David Dearnaley certifies that all conflicts of interest, including specific financial interests and relationships and affiliations relevant to the subject matter or materials discussed in the manuscript (eg, employment/affiliation, grants or funding, consultancies, honoraria, stock ownership or options, expert testimony, royalties, or patents filed, received, or pending), are the following: None.
Funding/Support and role of the sponsor: The trial was sponsored by UK