The study was early terminated due to low patient recruitment in already activated sites and difficult approval process in some of the anticipated countries. Thus, recruitment of the planned patient numbers in a reasonable time cannot be expected.

This will be an open, single-arm, international, multicentre, phase II imaging study to assess the predictive value of [68Ga]Ga PentixaFor PET imaging in primary and isolated secondary central nervous system lymphoma (CNSL) patients scheduled to undergo induction chemotherapy.

Inclusion Criteria:

1. Written informed consent obtained according to international guidelines and local laws by patient (or legally acceptable representative, if the patient is temporarily legally not competent owing to his/her disease). [Note: No invasive study-specific procedures may be carried out until this consent has been given.]

2. Patient aged 18 years or above (either sex).

3. Histologically confirmed primary or secondary CNSL based on cytology/flow cytometry of cerebrospinal fluid (CSF) or brain biopsy.

4. Disease exclusively located in the CNS (primary CNSL or secondary CNSL with isolated CNS relapse). Subjects who had undergone allogeneic stem cell transplant > 12 months prior to first dose of study drug, have no evidence of active graft versus host disease, and are not on systemic immunosuppressive therapy are allowed to participate in the study.

5. At least one measurable parenchymal lesion. [Note: parenchymal CNSL is a "must", and additional locations such as leptomeningeal disease are permitted.]

6. Previously untreated CNS disease. [Note: Previous or ongoing steroid treatment is permitted. Prophylaxis chemotherapy is not necessary, as induction chemotherapy will start within 72 hours after PTF-PET.]

7. At least one morphologically measurable lesion according to the IPCG criteria (Appendix 1).

8. Patients scheduled to undergo induction chemotherapy based on one of the following:

   High-dose methotrexate (HD-MTX)-based chemotherapy, ICE/DeVIC or High-dose cytarabine (HD-AraC)-based chemotherapy.

9. ECOG performance status ≤ 2 for patients aged ≥65 years; ECOG performance status ≤ 3 for patients aged <65 years.

10. Life expectancy of at least 3 months, as estimated by the investigator.

11. For women of child-bearing potential: negative pregnancy test.

12. For sexually active female patients of child-bearing potential: The patient agrees to take adequate contraceptive measures during study participation and also agrees to continue use of this method for the duration of the study and for 6 months after the last dose of PTF.

13. For male patients whose partner is of child-bearing potential: The patient is willing to ensure that he and his partner use effective contraception during the study and for 6 months after the last dose of PTF.

Exclusion Criteria:

1. Known hypersensitivity to [68Ga]Ga-PentixaFor or its components.

2. Contraindication for contrast-enhanced MRI as set out in the relevant institutional guidelines (e.g., pacemaker, defibrillator, aneurysm clip, metal in the body, renal insufficiency, severe claustrophobia etc.).

3. Contraindication for the use of gadolinium contrast for MRI.

4. Contraindication for PET according to institutional guidelines (weight-based, e.g. weight > 180 kg).

5. Inability to lie still for the entire imaging time.

6. Systemic lymphoma manifestation (outside the CNS).

7. Presence of active infection at screening or history of serious infection within the previous 6 weeks (except HIV infection: patients with HIV-associated primary CNSL are considered eligible).

8. Administration of another investigational medicinal product within the 30 days (or 5 excretion half-lives, whichever period is the longer) before first treatment with PTF.

   [Note: Re screening may be performed to accept washout of prior agents.]

9. Current toxicity of Grade >2 from previous standard or investigational therapies (grade according to the NCI Common Terminology Criteria for Adverse Events, version 5.0 (CTCAE 5.0).

10. For female patients: Pregnancy (existing or intended) or breast-feeding.

11. Renal impairment: Both of the following:

    Estimated glomerular filtration rate (eGFR) < 30 ml/min/1.73 m2 Creatinine clearance < 60 ml/min

12. Hepatic impairment: Both of the following:

    Aspartate aminotransferase (AST) > 3x upper limit of normal Alanine aminotransferase (ALT) > 3x upper limit of normal

13. Presence of any unstable systemic disease (including, but not limited to, active infection, uncontrolled hypertension, unstable angina, congestive heart failure, serious cardiac arrhythmia requiring medication, hepatic, renal or metabolic disease.

14. Presence of psychiatric disease, alcohol abuse or any other medical condition(s) that, in the opinion of the investigator, makes the patient unable to comply with study procedures and visits.

15. Patient weight ≤ 48 kg