The Axumin Scan (also termed: 18F-fluciclovine) — What is it?

This PET/CT study was approved by the FDA in May 2016 for evaluation of men with rising PSA’s after primary treatment with surgery or radiation.  It is a total body “functional” scan based on the cellular uptake of a synthetic leucine amino acid tagged with radioactive fluorine (F-18). Amino acids are building blocks of protein and a source of cellular energy — requirements for cellular proliferation. However, the radioactive synthetic leucine is not metabolized and is a more accurate reflection of transmembrane amino acid transport. The term “functional” implies that cellular adsorption is dependent on the cell’s metabolism. Hence the strength of the signal (the positron) to the scanner is dependent upon the size and the metabolic demands of the cancerous tissue. In contrast, a CT scan is a “morphologic” scan, displaying the only size and shape, as opposed to images reflecting a tumor’s metabolism. This distinction provides the Axumin scan greater sensitivity to discriminate cancer from non-cancer and to identify cancer in smaller lesions.

What kind of information can be expected from the Axumin scan.

A presentation at the Nuclear Medicine and Molecular Imaging Conference, 2016, Abstract #520, addressed the utility for staging of 86 patients, 55 with high-risk primary prostate cancer. This study compared scan findings with tissues pathology in 61 of 86 patients and serves as a validation of the accuracy of the scan for the detection of cancer. Regarding disease outside of the prostate area, in 88 – 93% the scan correctly identified cancer with 7.8% false positives. The scan was less accurate in identifying cancer in the prostate and prostate bed (i.e. 49% – 58%). [The mpMRI is the superior study for evaluation of the prostate and its surroundings.]

In patients with PSA values of <1.78 ng/mL the detection rate was 60% whereas of >1.78 ng/mL the rate was 80%. The conclusion: the Axumin PET/CT is predictive of regional lymph node and distant metastases in high-risk prostate cancer patients.”

How has the Axumin scan performed in PSA relapsed patients?

1)    “18F-Fluciclovine PET/CT for the Detection of Prostate Cancer Relapse,” Nanni et al., Clinical Nuclear Medicine, Aug 2015, addresses this issue, while in the same study compared the Axumin scan to the 11C-choline PET/CT.

Fifty patients were scanned within a month with both scans. The mean PSA at relapse was 3.2 ng/mL (range 0.24-15.6); the mean Gleason score was 7; and mean time from surgery 65 months.

Results for fluciclovine: Local Relapse, 5 patients; lymph node relapse, 9 patients; relapse in bone, 5 patients. At every locale the fluciclovine study was significantly superior to choline. The fluciclovine scan provided superior detection at all PSA levels between <1 ng/mL and >3 ng/ml. “Choline is incorporated into the proliferating cell’s cell wall. “The slow proliferation of prostate cancer cells, reflecting a slow membrane metabolism, produces a small amount of 11-C choline uptake and is the main reason for its low sensitivity.” (ibid)

2)    “Recurrent prostate cancer detection with anti-3-[18F]FACBC PET/CT [i.e. 18F-fluciclovine] comparison with CT, Odewole et al., Eur J Nucl Med Mol Imaging, 2016, offers an important clinical comparison since traditionally the CT scan has been the tool for staging at PSA recurrence. Fifty-three bone scan negative patients underwent both scans within 90 day of each other. The patients had had a full range of primary interventions.

Overall, of 53 patients the PET/CT had positive findings in 77.4% vs 18.9% of the CT Study. In the prostate bed the Axumin PET/CT was true positive in 31 of 51 men vs 4 of 51 for the CT. In extraprostatic regions the comparison of true positives was 12 of 41 patients vs 3 of 41 for the CT.  “Extraprostatic” referred to lesions in lymph nodes and bone. “The short axis of the smallest nodes considered positive on fluciclovine PET/CT was 0.4 cm, and on CT, 0.9 cm.

The median PSA at evaluation was 4 ng/mL. The whole body positivity rate at PSA 1-2 ng/ml was 77.8%  v 0%, and at PSA  >2-5 ng/ml was 91.7 % vs 41.7 % for fluciclovine vs CT, respectively.

Their conclusion: The diagnostic performance of fluciclovine PET/CT in recurrent prostate cancer is superior to that of the CT, and fluciclovine PET/CT provides better delineation of prostate from extraprostatic recurrence.“

Axumin scan results lead to a change from the pre-scan proposed treatment plan in a majority of cases.

A study at Emory University, Schreibmann et al, Int J Radiation Oncol Biol Phys, 2016, reported treatment plan changes in 41 patients based on imaging in patients having had both the 18F-Fluciclovine PET/CT and a high-resolution CT. “The inclusion of 18F-fluciclovine changed the planning volumes for 46 abnormalities (83%) of the total of 55, with 28 (51%) located lymph nodes, 11 (20%) in the prostate bed, 10 (18%) in the prostate, and 6(11%) in the seminal vesicles. Only 9 PET abnormalities were fully contained in the proposed CT based targets plan. In short, treatment planning targets were changed in 30 of 40 patients. Follow-up studies will be required to assess if the augmented treatments yield superior outcomes.” [Researchers at Emory University have been pioneers in the development of the 18F-fluciclovine PET/CT.]

A later study, again from Emory University, (Jani et al, J. Nucl Med, 2017) conducted a randomized comparison of salvage radiotherapy for recurrence after prostatectomy. Forty five men had double scanning, as described above, and in these men the final treatment planning was based on the PET/CT findings. In this group the PET/CT results lead to significant changes in treatment. These men were compared to 51 control patients whose treatment plans were based on CT imaging. “Longer follow-up is needed to determine the impact of 18F-fluciclovine PET on cancer control and late toxicity endpoint.”

Axumin scan availability information:

For informational about locations where the scan is available, Google Axumin.com then click on “Axumin.com.” The following screen includes a deep blue box “Find an Axumin imaging site.” As of mid-September there were 53 listed sites including contact information. For additional information about locations call 855-298-6461, option 3, since the list is being regularly updated.  Current information indicates that Medicare covers the cost of the scan, but this may vary according to location in the US.

Details regarding availability at Swedish Medical Center. (by David Djang, MD, Specialist in Nuclear Medicine, Swedish Medical Center, Seattle, WA)
  • Axumin (F18-fluciclovine) is the first FDA approved, widely available PET tracer specifically designed for imaging prostate cancer. The half-life and dosage of the tracer are approximately 110 min and 10 mCi, the same as the more common FDG tracer. Total scan appointment time will be relatively short; after tracer injection, the scan can begin in 3-5 min, and the scan itself will take 20-30 min.
  • For now, for people in the Seattle area, the tracer will be produced in Portland and driven up. At least in the beginning, appointment times will be limited to Wednesdays in the late afternoon. Within the next 6-12 months, it is expected that Axumin production will take place in Seattle, and then more appointment times will become available. Patients will be instructed to avoid significant exercise for a day prior to the scan, and not to eat or drink for at least 4 hours prior (though small amounts of water with medication will be fine).
  • Multiple imaging centers will be offering this new test. For those connected to or near the Swedish Cancer Institute, the PET/CT center can be contacted at 206 215 6487. Axumin PET/CT truly represents a step forward for men with suspected biochemical recurrence of prostate cancer.

 

BOTTOM LINE:  The management guidance provided by the Axumin PET/CT arises from its identification of the location of image-able cancer — locally, regionally, and systemically. This supports the design of appropriate treatment plans and is especially relevant for higher risk prostate cancers at PSA relapse after primary therapy.

%d bloggers like this: