This research is being done to find out if the study drug, 177Lu-PSMA-617, given before and during standard of care External Beam Radiation Therapy (EBRT) treatment, with a shorter course of Androgen Deprivation Therapy (ADT) (6 months) is (1) safe and effective compared to standard of care alone, and (2) can reduce the side effects caused by long-term (24 months) ADT in men with high risk localized prostate cancer.

Men with high-risk localized prostate cancer include those with stage cT3a or Grade Group 4/5 or Prostate Specific Antigen (PSA) >20 ng/mL, and the proportional rate of high-risk disease has increased to 20% of newly diagnosed patients in the US. These patients are currently recommended treatment with a combination of definitive radiotherapy and long-term androgen deprivation therapy (NCCN category 1) or radical prostatectomy with pelvic lymph node dissection. Radiotherapy most often consists of external-beam radiotherapy (EBRT) in 28 to 45 daily fractions with 1.5 to 3 years of ADT. Multiple phase III studies have shown a benefit in survival with long-term ADT. However, given the toxicities of long-term ADT, including fatigue, mood changes, sexual dysfunction, osteopenia, weight gain, diabetes and cardiovascular disease, many patients are reluctant to complete long-term ADT. This leads to significant demand for investigation of lower-toxicity alternatives to long-term ADT for patients with high-risk localized prostate cancer.

The combination of 177Lu-PSMA-617 with definitive EBRT and 6 months ADT for high-risk prostate cancer has the potential to increase the cumulative absorbed dose to the prostate, involved nodes, and micrometastatic disease, as well as decrease toxicity and improve QoL compared with EBRT and long-term ADT. ADT has been shown to increase radiosensitivity and PSMA expression of prostate cancer; therefore 6 months of ADT was selected to optimize the combination therapy while avoiding toxicities associated with long-term ADT. There are significant unknowns with respect to absorbed dose and toxicities of this potential combination of 177Lu-PSMA-617 and EBRT. In addition, the relative efficacy compared to EBRT plus long-term ADT is unknown. The investigators therefore propose a phase II randomized study of dosimetry, safety, and efficacy of Lu-177-PSMA-617, EBRT, and short-term ADT (6 months) in comparison with EBRT and long-term ADT (24 months).

Inclusion Criteria:

• Patient must have high-risk prostate cancer (HRPC) defined by presence of exactly one high-risk feature: cT3a OR Grade Group 4 or 5 OR PSA > 20 ng/mL.

• Histologic confirmation of adenocarcinoma of the prostate.

• Patient must have localized HRPC defined by conventional imaging (no N1 disease by CT or MRI). Patients with or without intra-pelvic nodal metastases by PSMA-PET may be included as long as not enlarged >10mm short axis by conventional CT size criteria.

• Patients must have PSMA-PET (68Ga-PSMA-11 or 18F-DCFPyL) with prostate tumor SUVmax > 10.

• Patient must qualify for definitive treatment of prostate cancer including EBRT as well as ADT (up to 45 days of prior ADT is allotted).

• Patient must be ≥ 18 years of age.

• Patient must have a life expectancy ≥ 24 months.

• Patient must have an Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2.

• Adequate bone marrow reserve and organ function as demonstrated by complete blood count and chemistry panel completed within the prior 6 weeks demonstrating:

  1. Platelet count of >100 x109/L
  2. White blood cell (WBC) count > 3,000/mL
  3. Neutrophil count of > 1,500/mL
  4. Hemoglobin ≥ 10 g/dL
  5. Estimated glomerular filtration rate (eGFR) > 50 mL/min based upon Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) equation. Due to safety concerns relating to renal clearance and toxicity of 177Lu-PSMA-617, patients with estimated GFR between 50 - 60 mL/min will require a 99mTc-TPA GFR test and only patients with non-obstructive pathology will be included in the study.
  6. Total bilirubin < 3 x ULN (except if confirmed history of Gilbert's disease)
  7. Serum albumin > 30 g/L
  8. Aspartate aminotransferase (AST) < 3 times the ULN

• For male patients with partners of childbearing potential, agreement to use barrier contraceptive method (condom) and to continue its use for 6 months from receiving the last dose of 177Lu-PSMA-617.

• Patient must have the ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

• Presence of a very high-risk feature: cT3b to T4 OR primary pattern 5 OR 2 to 3 high-risk features OR >4 cores with Grade Group 4 or 5.
• Any prior pharmacotherapy (with the exception of up to 45 days of ADT prior to randomization), radiation therapy, or surgery as treatment for prostate cancer. Any prior radiopharmaceutical therapy.
• Any prior radiation to the pelvis.
• Presence of N1 or M1 disease by conventional imaging (CT, MRI, and/or bone scan) or M1 disease by PSMA-PET (68Ga-PSMA-11 or 18F-DCFPyL). Lymph nodes with short axis > 8 mm by CT will be considered N1 by conventional imaging.
• Castration-resistant prostate cancer (CRPC).
• Patient receiving any other investigational agents.
• Patient is participating in a concurrent treatment protocol involving radiotherapy, surgery, or systemic anti-cancer agents.
• Inadequate bone marrow reserve and organ function as detailed in 5.1.10.
• Unable to lie flat during or tolerate PET/MRI, PET/CT or EBRT.
• Concurrent serious medical condition that, in the opinion of the Investigator, would impair study participation.
• Contraindication to receiving pelvic radiation, including history of or active inflammatory bowel disorders.
• Refusal to sign informed consent.