A Trial of 177Lu-PSMA617 Theranostic Versus Cabazitaxel in Progressive Metastatic Castration Resistant Prostate Cancer

TheraP: A Randomised Phase 2 Trial of 177Lu-PSMA617 Theranostic Versus Cabazitaxel in Progressive Metastatic Castration Resistant Prostate Cancer (ANZUP Protocol 1603)

This open label, randomised, stratified, 2-arm, multicentre, phase 2 trial aims to determine the activity and safety of Lu-PSMA vs cabazitaxel in men with progressive metastatic castration resistant prostate cancer

Despite recent advances in the treatment of prostate cancer, metastatic disease remains incurable.

Prostate specific membrane antigen (PSMA) is present in high quantities on the cell surface of prostate cancers, and is also further increased in metastatic hormone refractory carcinomas. PSMA is an attractive target for both imaging and treatment of prostate cancer. PSMA bound to the radioactive substance Gallium68 (GaPSMA) is rapidly being adopted for imaging prostate cancer using positron emission tomography (PET) scanning.

Radionuclide therapy is an approach for the treatment of cancer that uses tumour targeting agents to deliver high doses of radiation to sites of tumours. The PSMA molecule used for PET imaging can also be labelled with Lutetium177 (Lu177), a radioactive substance.

The aim of this study is to determine the activity and safety of LuPSMA radionuclide therapy.

Patients with metastatic prostate cancer who have progressed despite hormonal therapy and chemotherapy, will be randomised to receive either LuPSMA radionuclide therapy (up to a maximum of 6 cycles of therapy) or cabazitaxel chemotherapy (up to a maximum of 10 cycles of therapy).

200 participants will be recruited from sites across Australia.

The study will determine the effects on PSA response rate (primary endpoint), pain response, progression free survival, quality of life, and frequency and severity of adverse events. Correlative outcomes include associations between PET imaging and clinical outcomes, and biomarkers and clinical outcomes.

Inclusion Criteria:

1. Male aged 18 or older with metastatic adenocarcinoma of the prostate defined by:

   • Documented histopathology of prostate adenocarcinoma OR
   • Metastatic disease typical of prostate cancer (i.e. involving bone or pelvic lymph nodes or para-aortic lymph nodes)

2. Castration-resistant prostate cancer (defined as disease progressing despite castration by orchiectomy or ongoing Luteinizing Hormone-Releasing Hormone (LHRH) analog

3. Progressive disease with rising PSA on 3 consecutive measurements, and PSA ≥ 20 ng/mL

4. Target or non-target lesions according to RECIST 1.1

5. Prior treatment with docetaxel

6. Significant PSMA avidity on 68Ga-PSMA PET/CT, defined as a minimum uptake of SUVmax 20 at a site of disease, and SUVmax > 10 at sites of measurable disease ≥10mm (unless subject to factors explaining a lower uptake, e.g. respiratory motion, reconstruction artefact)

7. ECOG Performance status 0 to 2

8. Assessed by a medical oncologist as suitable for chemotherapy with cabazitaxel

9. Adequate renal function:

   • Cr Cl ≥ 40mL/min (Cockcroft-Gault formula)

10. Adequate bone marrow function:

    • Platelets ≥ 100 x10 billion /L
    • Hb ≥ 90g/L (no red blood cell transfusion in last 4 weeks)
    • Neutrophils > 1.5 x10 billion/L

11. Adequate liver function:

    • Bilirubin < 1.5 x upper limit of normal (ULN) (or if bilirubin is between 1.5-2x ULN, must have a normal conjugated bilirubin)
    • AST or ALT ≤ 2.0 x ULN (or ≤ 5.0 x ULN in the presence of liver metastases)

12. Estimated life expectancy > 12 weeks

13. Study treatment both planned and able to start within 21 days of randomisation

14. Willing and able to comply with all study requirements, including all treatments (cabazitaxel or Lu-PSMA); and, the timing and nature of all required assessments

15. Signed, written informed consent

Exclusion Criteria:

1. Prostate cancer with significant sarcomatoid or spindle cell or neuroendocrine small cell components
2. Site(s) of disease that are FDG positive with minimal PSMA expression defined as FDG intensity > 68Ga-PSMA activity OR 68Ga-PSMA SUVmax < 10
3. Sjogren's syndrome
4. Prior treatment with cabazitaxel or Lu-PSMA
5. Contraindications to the use of corticosteroid treatment
6. Active malignancy other than prostate cancer
7. Concurrent illness, including severe infection that may jeopardise the ability of the participant to undergo the procedures outlined in this protocol with reasonable safety
8. Presence of any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule, including alcohol dependence or drug abuse
9. Patients who are sexually active and not willing/able to use medically acceptable forms of barrier contraception