PSA for outcome prediction and posttreatment evaluation following radiation for prostate cancer: do we know how to use it?

Pharmacological Optimization of PSMA-Based Radioligand Therapy

Prostate cancer (PCa) is the most common malignancy in men of middle and older age. The standard treatment strategy for PCa ranges from active surveillance in low-grade, localized PCa to radical prostatectomy, external beam radiation therapy, hormonal treatment and chemotherapy. Recently, the use of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) for metastatic castration-resistant PCa has been approved. PSMA is predominantly, but not exclusively, expressed on PCa cells. Because of its high expression in PCa, PSMA is a promising target for diagnostics and therapy. To understand the currently used RLT, knowledge about pharmacokinetics (PK) and pharmacodynamics (PD) of the PSMA ligand and the PSMA protein itself is crucial. PK and PD properties of the ligand and its target determine the duration and extent of the effect. Knowledge on the concentration-time profile, the target affinity and target abundance may help to predict the effect of RLT. Increased specific binding of radioligands to PSMA on PCa cells may be associated with better treatment response, where nonspecific binding may increase the risk of toxicity in healthy organs. Optimization of the radioligand, as well as synergistic effects of concomitant agents and an improved dosing strategy, may lead to more individualized treatment and better overall survival.

DEFINING RECURRENCE AFTER RADIATION FOR PROSTATE CANCER

PURPOSE

We reviewed prostate specific antigen (PSA) definitions of recurrence after external beam radiation for prostatic cancer and related them to the definitions used for other treatment modalities.

MATERIALS AND METHODS

The literature on defining recurrence after external beam radiation, brachytherapy and prostatectomy for prostate cancer was reviewed through a MEDLINE search to ensure completeness and the inclusion of all pertinent information.

RESULTS

Although the definition, which is the current standard for estimating recurrence after external beam radiation, has proved to be a reasonable measure, alternative options that are more sensitive and specific have now been defined. Similar statistical testing and comparison must also be done for other treatment modalities since the choice of failure definitions has not been evaluated nearly as thoroughly for these therapies. As much as possible, outcome reporting should be done according to the same method to ensure fairness when comparisons are made. However, inherent differences between treatment modalities and their effect on PSA production must also be considered.

CONCLUSIONS

With the latest available information from patients with long-term followup PSA definitions of tumor recurrence after external beam radiation for prostatic cancer must again be reviewed in a consensus conference format. The application of a universal PSA definition of tumor recurrence across multiple treatment modalities should also be explored.

Individualized predictions of disease progression following radiation therapy for prostate cancer

PURPOSE

Following treatment for localized prostate cancer, men are monitored with serial prostate-specific antigen (PSA) measurements. Refining the predictive value of post-treatment PSA determinations may add to clinical management, and we have developed a model that predicts future PSA values and the time to future clinical recurrence for individual patients.

PATIENTS AND METHODS

Data from 934 patients treated between 1987 and 2000 were used to develop a comprehensive statistical model to fit the clinical recurrence events and patterns of PSA data. A logistic model was used for the probability of cure, mixed models were used for serial PSA measurements, and a proportional hazards model was used for recurrences. Data available through February 2001 were fit to the model, and data collected between February 2001 and September 2003 were used for validation.

RESULTS

T-stage, baseline PSA, and radiotherapy dosage are all associated with probability of cure. The risk of clinical recurrence in those not cured is strongly affected by the slope of PSA values. We show how the model can be used for individual monitoring of disease progression. For each patient the model predicts, based on baseline characteristics and all post-treatment PSA values, the probability of future clinical recurrences and future PSA values. The model accurately predicts risk of recurrence and future PSA values in the validation data set.

CONCLUSION

This predictive information on future PSA values and the risk of clinical relapse for each individual patient, which can be updated with each additional PSA value, may prove useful to patients and physicians in determining post-treatment salvage strategies.

Hazards of dose escalation in prostate cancer radiotherapy

PURPOSE

To assess the benefit of escalating the dose in definitive prostate cancer radiotherapy vs. the associated risk of complications.

MATERIALS AND METHODS

Between 1987 and 1999, 1087 patients with clinical Stage T1b-T3 adenocarcinoma of the prostate were definitively irradiated without hormonal therapy and had a pretreatment serum prostate-specific antigen (PSA) and Gleason score recorded. The median follow-up was 65 months. Doses ranged from 64 to 78 Gy, with the treatment techniques corresponding to the year of therapy and the prescribed dose. A total of 301 patients were treated on a randomized protocol to either 70 or 78 Gy. Also, 163 patients were treated with three-dimensional conformal therapy and had dose-volume histograms available for review.

RESULTS

Tumor stage, grade, pretreatment PSA level, and radiation dose were all independent predictors of PSA disease-free survival (PSA-DFS) in multivariate analysis. The hazard rate for biochemical failure peaked at 1.5-3 years after radiotherapy. Although a statistically significant dose effect on PSA-DFS was found in the pretreatment PSA levels of those with both < or =10 ng/mL and >10 ng/mL, in those with a pretreatment PSA < or =10 ng/mL, the improvement in outcome was only seen going from a dose level of 64-66 Gy to 68-70 Gy with a 5-year PSA-DFS rate of 66% vs. 81% (p <0.0001). This was also confirmed by the data from the randomized patients who showed no difference in outcome whether treated to 70 Gy or 78 Gy. In patients with a pretreatment PSA level >10 ng/mL, a statistically significant improvement was found in disease-free outcome among the 64-66-Gy, 68-70-Gy, and 78-Gy levels. PSA-DFS was approximately 50% better at each higher dose level at 5 and 8 years after treatment. The dose had a statistically significant impact in both intermediate- and high-risk groups. Rectal morbidity was both dose and volume related. Although at 5 years after therapy, the Grade 2-3 rectal complication rate was twice as high for patients treated to 78 Gy than to 70 Gy, 26% vs. 12%, this risk could be markedly diminished by adhering to dose-volume constraints.

CONCLUSIONS

In intermediate- and high-risk prostate cancer patients, although it appears that radiation-dose escalation may improve PSA-DF outcome, the price paid in treatment morbidity can be high without adequate attention to dose-volume constraints of normal tissue. Care must be taken to consider not only the hazard of tumor recurrence but also that of complications.

Quality-of-care indicators for early-stage prostate cancer

PURPOSE

Decisions regarding treatment for early-stage prostate cancer are frustrated not only by inadequate evidence favoring one treatment modality but also by the absence of data comparing quality among providers. In fact, the choice of provider may be as important as the choice of treatment. We undertook this study to develop an infrastructure to evaluate variations in quality of care for men with early-stage prostate cancer.

METHODS

We enlisted several sources to develop a list of proposed quality-of-care indicators and covariates. After an extensive structured literature review and a series of focus groups with patients and their spouses, we conducted structured interviews with national academic leaders in prostate cancer treatment. We then convened an expert panel using the RAND consensus method to discuss and rate the validity and feasibility of the proposed quality indicators and covariates.

RESULTS

The panel endorsed 49 quality-of-care indicators and 14 covariates, which make up our final list of candidate measures. Several domains of quality are represented in the selected indicators, including patient volume, pretreatment referrals, preoperative testing, interpretation of pathology specimens, and 10-year disease-free survival. Covariates include measures of case-mix, such as patient age and comorbidity.

CONCLUSION

This study establishes a foundation on which to build quality-of-care assessment tools to evaluate the treatment of early-stage prostate cancer. The next step is to field-test the indicators for feasibility, reliability, validity, and clinical utility in a population-based sample. This work will begin to inform medical decision-making for patients and their physicians.

A retrospective analysis of the results of p(65) + Be neutrontherapy for the treatment of prostate adenocarcinoma at the cyclotron of Louvain-la-Neuve. Part I: Survival and progression-free survival

PURPOSE

To retrospectively evaluate survival, progression-free survival (PFS) and biological response in a series of patients irradiated with mixed neutron/photon beams for locally advanced prostate cancer in our institution.

PATIENTS AND METHODS

Three hundred and eight patients were treated between January 1990 and December 1996. Fifty-five of these were recruited for pT3 or pN1 tumors after radical prostatectomy. Neoadjuvant androgen deprivation was given in 106 patients. The treatment protocol consisted of a mixed photon/neutron irradiation in a two-to-three proportion, up to a total equivalent dose of 66 Gy (assuming a clinical RBE value of 2.8). Pre- and post-treatment PSA determinations were available in practically all cases. Study endpoints were overall survival (OAS) and progression-free survival (PFS). The Cox proportional hazard regression model was used to investigate the prognostic value of baseline characteristics on survival and progression-free survival were a progression was defined as local, regional, metastatic or biological progression. Mean age was 69 years (49-86); mean pretreatment PSA was 15 (0.5-330) in all patients and 14 (0.5-160) in those receiving neoadjuvant hormonotherapy; seven patients only had an initial PSA < or = 4 ng/mL; 15% were T1, 46% were T2, 28% were T3 or pT3 and 4% were T4 (7% unspecified); WHO grade of differentiation was I in 38%, II in 38% and III in 14% (5% unspecified).

RESULTS

The median follow-up was 2.8 years (0-7.8). Five-year overall survival (OAS) was 79% (95% CI: 71-87%) and 5-year progression-free survival (PFS) was 64% (95% CI: 54-74%) for the entire series. PFS in patients with an initial PSA > or = 20 ng/mL was the same. PFS could be predicted by two optimal Cox regression models, one including histological grade (p = 0.003) and initial PSA (p = 0.0009) as cofactors, the other including histological grade (p = 0.003) and T stage (p = 0.02). The main prognostic factors for overall survival were PSA and age. Biological responses with PSA < 1.5 ng/mL, < 1 ng/mL and < 0.5 ng/mL at any time after treatment were documented in 70%, 61% and 47% of the patients, respectively.

CONCLUSION

Five-year OAS was 79%, PFS was 64%, and biological response was 70% for prostate cancer patients treated with mixed photon/neutron beams as applied at Louvain-la-Neuve, which are good results as compared with the literature. The usual prognostic factors were confirmed.

Postradiotherapy prostate biopsies: what do they really mean? Results for 498 patients

PURPOSE

Postradiotherapy (RT) prostate biopsies are prone to problems in interpretation. False negatives due to sampling error, false positives due to delayed tumor regression, and indeterminate biopsies showing radiation effect in residual tumor of uncertain viability are common occurrences.

METHODS AND MATERIALS

A cohort of 498 men treated with conventional RT from 06/87-10/96 were followed prospectively with systematic transrectal ultrasound (TRUS)-guided post-RT prostate biopsies, starting 12-18 months after RT. If there was residual tumor but further decline in serum prostate-specific antigen (PSA), biopsies were repeated every 6-12 months. Patients with negative biopsies were rebiopsied at 36 months. Residual tumor was evaluated for RT effect and proliferation markers. The 498 men had 978 biopsies. Median time of the first biopsy (n = 498) was 13 months, biopsy #2 (n = 342) 28 months, biopsy #3 (n = 110) 36 months, biopsy #4 (n = 28) 44 months, and biopsy #5 (n = 4) 55 months. Median follow-up is 54 months (range 13-131). One hundred seventy-five patients (34%) had prior hormonal therapy for a median of 5 months (range 1-60).

RESULTS

Clinical stage distribution was T1b: 46; T1c: 50; T2a: 115; T2b/c: 170; T3: 108; T4: 11; Tx: 1. Distribution by Gleason score was: 28% Gleason score 2-4; 42%: 5-6; 18%: 7; and 12%: 8-10. Seventy-one men have died, 26 of prostate cancer and 45 of other causes. Actuarial failure-free survival by T stage at 5 years is T1b: 78%; T1c: 76%; T2a: 60%; T2b/c: 55%; T3: 30%; and T4: 0%. Actuarial freedom from local failure at 5 years is T1b: 83%; T1c: 88%; T2a: 72%; T2b/c: 66%; T3: 58%; and T4: 0%. The proportion of indeterminate biopsies decreases with time, being 33% for biopsy 1, 24% for biopsy 2, 18% for biopsy 3, and 7% for biopsy 4. Thirty percent of indeterminate biopsies resolved to NED status, regardless of the degree of RT effect, 18% progressed to local failure, and 34% remained as biopsy failures with indeterminate status within the time frame of this report. Positive staining for proliferation markers was associated with both subsequent local failure and also any type of failure. In multivariate analysis, only PSA nadir (p = 0.0002) and biopsy status at 24-36 months (p = 0. 0005) were independent predictors of outcome.

CONCLUSIONS

Post-RT prostate biopsies are not a gold standard of treatment efficacy, but are an independent predictor of outcome. Positive immunohistochemical staining for markers of cellular proliferation is associated with subsequent local failure. Indeterminate biopsies, even when showing marked RT effect, cannot be considered negative.

Defining biochemical cure for prostate carcinoma patients treated with external beam radiation therapy

BACKGROUND

The authors retrospectively reviewed their institution's long term experience with conventional external beam radiation therapy (RT) for localized prostate carcinoma to identify criteria associated with long term biochemical cure.

METHODS

Between January 1987 and December 1994, 871 patients were treated with external beam RT alone for clinically localized prostate carcinoma at William Beaumont Hospital, Royal Oak, Michigan. All patients received only external beam RT to a median total dose of 66.6 grays (Gy) (range, 59.4-70.4 Gy). No patient received hormonal therapy unless treatment failure was documented. The median follow-up was 5.0 years (range, 0. 2-11.8 years). Biochemical failure was defined according to the American Society for Therapeutic Radiology and Oncology Consensus Panel definition.

RESULTS

In the entire study group, 380 patients experienced biochemical failure at a median interval of 1.5 years after the completion of RT. The 5-year and 7-year actuarial rates of biochemical control were 50% and 48%, respectively. On multivariate analysis, a higher pretreatment prostate specific antigen (PSA) level, higher Gleason score, higher clinical T classification, higher nadir level, and shorter time interval to nadir all were associated significantly with biochemical failure (P < 0.001). The median intervals to biochemical failure for patients with pretreatment PSA levels </= 3.9 ng/mL, 4.0-19.9 ng/mL, and >/= 20.0 ng/mL were 2.2 years, 1.5 years, and 1.2 years, respectively (P < 0. 001). The median intervals to biochemical failure for patients with Gleason scores of 2-4, 5-7, and 8-10 were 1.8 years, 1.5 years, and 1.1 years, respectively (P < 0.001). Only 6 patients failed beyond 5 years after treatment even though 136 patients were at risk for failure beyond this point. When restricting analysis to 643 patients (74%) with >/= 3 years of PSA follow-up, the median nadir level for biochemically controlled patients was 0.6 ng/mL and occurred at a median interval of 1.9 years after RT versus a median nadir level of 1.3 ng/mL (P = 0.002) occurring at a median interval of 1.0 years (P < 0.001) in those patients who experienced biochemical failure. Patients were divided into subgroups based on their PSA nadir level and time to nadir. The 5-year actuarial biochemical control rates for patients with nadir values of </= 0.4 ng/mL, 0.5-0.9 ng/mL, 1. 0-1.9 ng/mL, 2.0-3.9 ng/mL, and >/= 4.0 ng/mL were 78%, 60%, 50%, 20%, and 9%, respectively (P < 0.001). The 5-year actuarial biochemical control rates for patients who reached their nadir at < 1.0 years, 1.0-1.9 years, 2.0-2.9 years, and >/= 3.0 years were 30%, 52%, 64%, and 92%, respectively (P < 0.001). All 52 patients who achieved a nadir of </= 0.4 ng/mL and required >/= 2.0 years to reach this nadir had biochemically controlled disease.

CONCLUSIONS

These results suggest that a patient has a high likelihood of biochemical cure after treatment for prostate carcinoma with conventional doses of external beam RT if he has not demonstrated biochemical failure within 5 years of treatment. Patients with lower pretreatment PSA levels and lower Gleason scores may require longer follow-up than those with less favorable characteristics to achieve the same certainty of cure. Patients who achieve a PSA nadir </= 0.4 ng/mL and require >/= 2.0 years to reach this nadir have the highest probability of cure.

The importance of adequate follow-up in defining treatment success after external beam irradiation for prostate cancer

PURPOSE

We reviewed our institution's experience treating patients with localized prostate cancer with external beam radiation therapy (RT) to determine how differences in the length of follow-up affect the determination of treatment outcome using the American Society for Therapeutic Radiology and Oncology (ASTRO) Consensus Panel Definition of biochemical failure (BF).

METHODS AND MATERIALS

From January 1987 through December 1997, 1109 patients with localized prostate cancer were treated with definitive external beam RT at William Beaumont Hospital, Royal Oak, Michigan. All patients received external beam RT to a median total prostate dose of 66.6 Gy (range: 59.4-70.4 Gy). A total of 1096 patients (99%) had sufficient prostate-specific antigen (PSA) follow-up to determine their biochemical status. To test the impact of differences in follow-up on the calculation of BF, 389 patients with at least 5 years of PSA follow-up were selected as the reference group for the initial analysis. BF was then retrospectively determined using the Consensus Panel definition at yearly intervals, ignoring the remainder of each patient's follow-up. The median follow-up for this group of patients was 6.6 years (range: 5.0-11.6 years). In a second analysis, patient cohorts were randomly selected with varying median PSA follow-up intervals in order to more accurately represent a population whose follow-up is distributed continuously over a defined range. Seven cohorts were randomly selected with 200 patients in each cohort. Cohorts were individually identified such that half of the patients (100) had 2 years or less follow-up than the stated time point for analysis and half (100) had up to 2 years more follow-up than the time point chosen for analysis. For example, in the cohort with a median follow-up of 3 years, 100 patients with a PSA follow-up from 1 to 3 years were randomly selected, and 100 patients with a follow-up from 3 to 5 years were randomly selected, thus generating a median follow-up of 3 years for this cohort (range: 1 to 5 years). This process was repeated five times for five random samples of seven cohorts each. Biochemical failure was calculated according to the Consensus Panel definition.

RESULTS

In the first analysis, significantly different rates of biochemical control (varying by 6-21%) were calculated for the same actuarial year chosen for analysis depending only upon the length of follow-up used. For example, the 3-year actuarial rate of biochemical control (BC) varied from 71% when calculated with 3 years of follow-up versus 50.4% with 7 years (p < 0.01). These differences in actuarial rates of BC were observed in all subsets of patients analyzed (e.g., PSA < 10, Gleason < or = 6, n = 132,p < 0.001; PSA < 10, Gleason > or = 7, n = 33, p = 0.03; PSA > or = 10, Gleason < or = 6, n = 109, p < 0.001; and PSA > or = 10, Gleason > or = 7, n = 72, p = 0.002). The absolute magnitude of the difference in actuarial rates of BC was greatest during years 2 (range 18-30%), 3 (range 16-25%), and 4 (range 15-24%) after treatment. In the second analysis using median PSA follow-ups (as defined above), statistically significant differences in actuarial rates of BC were again observed. For example, the 3-year actuarial rate of BC varied from 74.8% with a median follow-up of 2 years versus 49.2% with a median follow-up of 6 years. These dramatic differences in BC were still observed beyond 5 years.

CONCLUSION

When the ASTRO Consensus Panel definition of BF is used to calculate treatment success with external beam RT for prostate cancer, adequate follow-up is critical. Depending upon the length of time after treatment, significantly different rates of BC (varying by 15% to 30%) can be calculated for the same time interval chosen for analysis. These results suggest that data should only be reported if the length of follow-up extends at least beyond the time point at which actuarial results are examined for the majority of patients.