Outcomes with metastasis-directed therapy (MDT) and fixed-duration systemic therapy in oligometastatic hormone-sensitive prostate cancer (omHSPC)

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Background: Intensification of systemic therapy beyond ADT, with use of novel hormonal agents (NHAs), and radiotherapy (RT) to the prostate have a proven survival benefit in mHSPC. MDT has shown benefit in delaying need for ADT in omHSPC in phase 2 trials. Combination of fixed-duration systemic therapy with MDT (and RT to the prostate in de novo mHSPC) may produce long-term remission and treatment-free survival in selected patients with omHSPC. Methods: Patients with de novo or recurrent omHSPC treated at our institution between 2010-2020 with MDT (+/- prostate RT if de novo) and a fixed duration of systemic therapy completed by September 2022 were identified. There was no limit on number of metastases as long as all sites could be treated with MDT in the view of the treating physician. Oligometastases were defined as bone or soft tissue lesions beyond the pelvic lymph nodes identified on conventional scans (CT, bone scan, MRI) or PET (fluciclovine or PSMA). The primary outcome was freedom from biochemical recurrence (BCR), defined as PSA of >0.02 (if the patient had undergone prior radical prostatectomy) or >2+nadir (if the patient underwent RT) after completion of systemic therapy. Testosterone recovery was defined as serum testosterone >150ng/dL attained after completion of systemic therapy. BCR-free survival after completion of systemic therapy was estimated using the Kaplan Meier method. Results: 32 patients were included. Median age at diagnosis of mHSPC was 67 (range 52-78). 12 patients (38%) had de novo mHSPC while 20 (63%) had oligorecurrent HSPC. Detection of omHSPC was by conventional scans in 23 patients (72%) and by PET only in 9 (28%), and median number of oligometastases was 1 (range 1-6). Median PSA at start of therapy for omHSPC was 8.2ng/mL (range 0.4-1244), with systemic therapy most commonly comprising of ADT and a NHA (abiraterone, enzalutamide, apalutamide, n=26 [82%]); 6 patients (19%) had ADT alone. Median duration of systemic therapy was 24 months (range 6-36), with 3 men (9%) having received prior systemic therapy for mHSPC. MDT consisted of external beam RT (EBRT, n=10, 31%), EBRT + stereotactic body radiotherapy (SBRT, n=8, 25%), or SBRT alone (n=14, 44%). At a median follow-up of 44 months (range 24-127) and 20 months (2-103) after start and completion of systemic therapy respectively, 9 patients (28%) had BCR and 23 (72%) remained free of BCR, of whom 13 (57%) had testosterone recovery. The estimated 2-year BCR-free survival after completion of systemic therapy was 73% (95% CI 51-86). Conclusions: In this carefully selected cohort of men with omHSPC, estimated 2-yr BCR-free survival after completion of therapy was >70% with ~2 years of ADT +/- NHA along with MDT +/- prostate RT (if de novo). Longer follow-up is needed to determine whether this translates to a durable treatment-free remission, and possibly cure, in these patients with omHSPC.

Circulating tumor DNA and homologous recombination deficiency in bone-predominant mCRPC prior to radium-223 therapy

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Background: Radium-223 (Ra-223) is a bone-seeking alpha emitter that induces double-stranded DNA breaks, and the homologous recombination (HR) pathway is critical for repairing these breaks. While prior studies suggested that metastatic castrate-resistant prostate cancers (mCRPC) patients (pts) with HR-deficient (HRD+) tumors may be more likely to benefit from Ra-223, obtaining tissue for next generation sequencing to identify HRD+ is challenging in pts with bone-predominant disease. We hypothesized that circulating tumor DNA (ctDNA) would allow for broader identification of HRD+ to assess association with clinical outcomes in a real-world cohort. Methods: We identified 135 mCRPC pts treated with Ra-223 at our institution between 2013 and 2021. Pts who initiated another anti-tumor therapy within 60 days of Ra-223 treatment were excluded; pts continuing hormonal agents initiated >60 days prior were included. ctDNA isolated from pre-treatment plasma underwent ultra-low-pass whole genome sequencing to estimate tumor fraction (TF). Additionally, targeted panel sequencing using an institutional prostate cancer-specific panel of 319 genes with duplex sequencing (utilizing unique molecular identifiers) for error suppression was used to identify germline or somatic deleterious alterations in HR pathway genes. The primary outcome was association between HRD status and completion of fewer than 6 cycles (as a proxy for early clinical progression), assessed using logistic regression. Results: The median age was 61 (IQR, 56-67) years, median pretreatment prostate-specific antigen (PSA) level was 26.2 (IQR, 8.1-84.1) ng/mL, and median TF was 4% (IQR, 3-6%). 97% of pts (n=131) previously received a novel antiandrogen, and 63% (n=85) received prior taxane. 17% (n=23) were HRD+, and 59% (n=80) completed 6 cycles of Ra-223. On multivariable analysis, HRD+ was associated with decreased likelihood of completing 6 cycles compared to HRD- (adjusted odds ratio [AOR] 0.16, 95% confidence interval [CI] 0.05-0.48, P=0.001). 22% (n=5) of HRD+ pts completed 6 cycles compared to 67% (n=75) of HRD- pts. Additional factors associated with decreased likelihood of completing 6 cycles included a higher pretreatment TF (AOR 0.69, 95% CI, 0.48-0.97, P=0.034) and prior taxane use (AOR 0.41, 95% CI, 0.18-0.91, P=0.028), but not pretreatment PSA ( P=0.574). Conclusions: Targeted panel sequencing with error suppression from ctDNA identified HRD+ in mCRPC pts with bone-predominant disease and low median TF at a similar frequency as reported from tissue. In our cohort, HRD+ was prognostic of early clinical progression with Ra-223. Further work is in progress to understand the association of other ctDNA-derived features, including assessment of genomic signatures and transcriptional binding sites, in the setting of Ra-223 therapy. DF/HCC IRB protocol 18-135.

Clinical implementation of 177Lu-PSMA-617 (LuPSMA) at a major academic center: Initial experiences

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Background: LuPSMA received FDA approval in March 2022 for patients with PSMA-positive metastatic castrate-resistant prostate cancer (mCRPC). Clinical implementation of this treatment requires multidisciplinary team (MDT) involvement and has been beset by challenges in drug supply. We established a joint DFCI GU/Nuclear Medicine Tumor Board (GU-NM TB) to review patients for therapy, and our initial experiences are described. Methods: A joint GU-NM TB was established. All patients with mCRPC who had received at least one prior chemotherapy and a novel hormonal agent were considered eligible and referred to TB through an online referral system after undergoing PSMA-PET/CT. Case details, including prior treatment history, performance status and organ function, and PET/CT imaging were reviewed at TB, with patients either being approved, deferred, or declined for LuPSMA therapy. Patients were scheduled for therapy on a first-come first-served basis. Treatment was delivered per standard-of-care at 180-200 millicurie doses every 6 weeks within NM. A questionnaire was sent to 25 referring physicians 2 months after implementation of the TB to evaluate the referral process. Results: Between May-September 2022, a total of 108 patients were referred for LuPSMA therapy. Median age at time of referral was 73 (range 52-93), and 90% of patients were Caucasian. Median duration between PSMA-PET/CT and TB review was 10 days (IQR 6-17). 84 patients (78%) were approved for therapy, 16 (15%) were deferred and 7 (6%) were declined (reasons including absence of prior chemotherapy, high risk for toxicities, poor performance status); 1 patient died before TB review. Prior therapies included docetaxel (84%), cabazitaxel (56%), abiraterone (67%), enzalutamide (57%), darolutamide (23%), radium-223 (21%) and apalutamide (7%). Median number of prior treatments was 4 (range 2-12). Sites of disease on PSMA-PET/CT included bone (81%), pelvic lymph nodes (42%), extrapelvic lymph nodes (88%), lung (27%) and liver (22%). As of September 2022, a total of 40 patients (48%) have received at least 1 cycle of therapy and 17 (20%) have received 2 cycles; 6 patients (7%) approved for therapy died before receiving 177Lu-PSMA-617. Of the patients that have received 1 cycle of therapy, median duration between TB acceptance and C1 was 52 days (range 32-114). Out of 13 survey respondents, all 13 (100%) reported that their overall experience of the referral process was positive or very positive, and 12 (92%) noted that the Tumor Board had provided additional clinical insights on occasion or frequently. Conclusions: Due to drug supply shortages, <50% of patients approved for LuPSMA therapy have started treatment to date. Median time between TB approval and start of therapy was 7-8 weeks, with 7% of patients dying before receiving therapy. Establishment of a GU-NM TB to review cases and facilitate treatment was viewed favorably by treating physicians.