FDA Approves Radioactive Imaging Agent Axumin in Recurrent Prostate Cancer

Libero Marzella, MD, PhD

The radioactive imaging agent, fluciclovine F18 (Axumin), was approved by the FDA for use in positron emission tomography (PET) scans in men with suspected recurrence of prostate cancer whose prostate-specific antigen (PSA) levels rise following prior treatment.

With the approval of the agent, clinicians hope to better determine the location of the recurrence in the prostate, as this defines optimal choice of therapy. Standard imaging tests used to determine identification of sites of recurrence have low diagnostic accuracy, so more accurate techniques are needed.¹

“Imaging tests are not able to determine the location of the recurrent prostate cancer when the PSA is at very low levels,” said Libero Marzella, MD, PhD, of the FDA’s Center for Drug Evaluation and Research and director of the Division of Medical Imaging Products, in a statement. “Axumin is shown to provide another accurate imaging approach for these patients.”

It is estimated that up to one-third of patients who receive curative treatment after a diagnosis of primary prostate cancer will experience recurrence within 10 to 15 years following primary treatment.²

The approval was granted based on 2 safety and efficacy studies involving Axumin scans in men with suspected recurrent disease. In the first study, 105 Axumin scans were compared with the histopathology samples obtained by prostate biopsy and by biopsies of suspicious imaged lesions in patients with suspected recurrent disease. In the blinded study, radiologists read the scans initially, with subsequent review by 3 independent radiologists.

A second study determined the agreement between Axumin scans and C11 choline, which is an approved PET imaging agent, involving patients with median PSA values of 1.44 ng/mL. To determine consistency, on-site radiologists read the scans initially. Their diagnoses were confirmed by 3 independent, blinded radiologists who read the scans in this second blinded study. The researchers report that the independent scan readings were generally consistent with one another, confirming the results of the on-site scan readings. Both studies supported the safety and efficacy of the agent for imaging prostate cancer in men with elevated PSA levels following prior treatment.

PET scans are a well-established non-invasive imaging technique that uses the radiotracer [18F]flouro 2-deoxyglucose (FDG) for many tumor types. However, this agent is not widely used in imaging prostate cancer because of poor uptake and high urinary excretion limiting imaging quality.3

The other PET radiotracer that is available, C11 choline, has been shown to improve detection in men with biochemical recurrent prostate cancer, but its 20-minute half-life limits use to medical centers with on-site C11 production capability.

Axumin is a synthetic amino acid that is actively transported into prostate cancer cells by amino acid transporters. It is not metabolized, nor is it incorporated into newly synthesized proteins. Imaging studies have demonstrated that Axumin is preferentially taken up into prostate cancer compared with surrounding normal tissue and visualization is not obscured by bladder uptake.

The agency advises that the agent should be handled with appropriate safety measures to minimize radiation exposure to patients and healthcare providers during administration. Image interpretation errors can occur with Axumin PET imaging. A negative image does not rule out the presence of recurrent prostate cancer and a positive image does not confirm the presence of recurrent prostate cancer. Clinical correlation, which may include histopathological evaluation of the suspected recurrence site, is recommended.

The most commonly reported adverse events in patients are injection site pain, redness, and a metallic taste in the mouth.

1. Choueiri TK, Dreicer R, Paciorek A, Carroll PR, Konety B. A model that predicts the probability of positive imaging in prostate cancer cases with biochemical failure after initial definitive local therapy. J Urol. 2008;179(3):906—910.
2. Freedland SJ, Moul JW. Prostate specific antigen recurrence after definitive therapy. J Urol. 2007;177(6):1985—1991.
3. Abdellaoui A1, Iyengar S, Freeman S. Imaging in prostate cancer. Future Oncol. 2011;7(5):679—691.