PET, CT images pinpoint recurrent prostate cancer

Anaheim, CA-Combined positron emission tomography and computed tomography imaging using [11C]choline as a tracer may be useful in detecting prostate cancer recurrence and, more important, may help clinicians to determine whether the recurrence is local or metastatic, according to a German study presented at the AUA annual meeting here.

"It is a promising tool to detect clinical relapse. Early detection of the return of the cancer can be an advantage," first author Ludwig Rinnab, MD, of the department of urology and pediatric urology at the University of Ulm, told Urology Times.

"We know that this particular study has limitations in that the sample was homogeneous, but we wanted to show that we have the ability to clarify the recurrence; that we can determine whether it is local or systemic," he added. "That information allows treatment decisions. A patient with local recurrence may benefit from brachytherapy, but a patient with metastatic recurrence would need hormone deprivation."

"It is well established that patients with prostate cancer show an increased uptake of choline in cancerous cells and that this uptake can be imaged with computed tomography," Dr. Rinnab said.

High sensitivity, specificity

Core study data showed that at a PSA of 2.5 ng/mL, sensitivity of the scan was 91% (95% Confidence Interval [CI]=0.71, 0.99) and specificity was 50% (95% CI=0.16, 0.84). The data drew a reasonably complete portrait of the tracer's current abilities. Patients presenting with positive scans had a mean PSA of 3.62 ng/mL (range, 0.5 to 13.1 ng/mL) compared to a mean 0.9 ng/mL PSA (range, 0.41 to 1.40 ng/mL) in patients showing with negative scans. The test proved positive in 100% (17/17) of men with PSA 1.5 to 2.5 ng/mL. It was also positive in 100% (11/11) of men with PSA 2.5 to 5.0 ng/mL and 100% in those with PSA <5.0 ng/mL.

Dr. Rinnab reiterated that the test was being studied as a means of determining the nature of recurrence, not for detecting recurrence.

He explained that [11C]choline is taken into malignant cells, which upregulate choline kinase and trap it in their membranes. The tracer is one of several that have been studied during the past decade. Others include FDG, a radioactive sugar tracer, C-11 acetate, and F-18 fluorodihydrotestosterone (FDHT). To date, [C11]choline appears to have the most utility in the prostate cancer setting. One of the advantages of [C11]choline is that it is already a commonly used tracer that should be available at most institutions, at least in Europe, Dr. Rinnab added.

Given the current data, he noted that clinicians probably would benefit by initiating the PET/CT scan with [C11]choline in patients with PSA levels of 2.5 ng/mL or higher.

Research is continuing with the goal of making the procedure more sensitive and specific. One moderator of the session suggested that the goal of research on [C11]choline and other similar research should be to differentiate local recurrence from metastatic recurrence at PSA levels of 0.9 ng/mL or lower, a level at which treatments such as hormone ablation seem to be most beneficial.