PET/CT in prostate cancer influences staging, treatment strategy

Prostate-specific antigen measurements are considered a useful organ-specific marker, but they are not necessarily an adequate tumor marker. PET/CT in combination with PSA levels can play a significant role in detecting and staging prostate cancer, according to two presentations Sunday at RSNA 2008.

Dr. Nghi Nguyen presented his multi-institutional group's work on the utility of PET/CT in staging and restaging prostate cancer. Nguyen is from St. Louis University Hospital, where the research was conducted. The study's lead author, Dr. Kahlid Taalab Jr., is now based in Cairo.

For this retrospective research, 21 prostate cancer patients underwent FDG-PET/CT studies for staging and 29 had restaging. For recurrence, PSA was defined as greater than 0.4 in patients with prior radical prostatectomy and greater than 1.0 in patients who had undergone prior hormonal therapy, radiation therapy, or chemotherapy.

The scans were reviewed by two nuclear medicine physicians, with a third reading if the findings were equivocal. The reference standard was histopathology, clinical, or imaging follow-up.

The results indicated that PET/CT correctly identified prostate cancer or metastases in 48% of the patients who were imaged for staging purposes. In the 29 who underwent restaging, three were deemed tumor-free, while 26 were considered clinically suspicious for recurrent disease.

Of these 26, PET/CT was false negative in 35% of the cases but suspicious for cancer in 65%. Of the 17 patients with these suspicious findings, malignancy was confirmed in 42%. Of the total 50 patients, PET/CT revealed a second, previously unknown cancer in 8%.

In a second report, Dr. Carlos Trampal and colleagues at the Instituto d'Alta Tecnologica in Barcelona evaluated the usefulness of carbon-11 choline PET/CT for detecting recurrent prostate cancer in patients with increased serum PSA levels.

"Serum PSA level is the most sensitive tool for (detecting) prostate cancer recurrence, but it's not able to identify the signs of recurrence," Trampal said. "In addition, conventional imaging techniques have low sensitivity for detecting prostate recurrence. PET with C-11 choline has shown promising results for detecting recurrent cancer."

The patient population consisted of 13 men with clinically elevated serum PSA (mean of 17.92 ng/mL). Whole-body PET/CT scans were done after a 740-MBq injection of C-11 choline. Imaging findings were classified as positive or negative based on pathologic tracer uptake using visual and semiquantitative analysis, Trampal said. PET results were validated with histology or clinical/radiological follow-up.

PET/CT with C-11 choline showed pathological uptake consistent with recurrence in nine patients. Among the nine, five had local recurrence, three had distant disease, and one patient had local recurrence plus multiple nodal involvment.

Based on the PET findings, patients were sent for either localized radiation treatment or systemic therapy (hormonal or chemotherapy). Trampal reported that all patients showed decrease in serum PSA levels after treatment. PET results were negative in four patients who did not have receive treatment, and no evidence of recurrence was seen on follow-up between six and 12 months.

Overall, C-11 choline detected disease in 87.5% of the patients with a PSA level that was greater than 3 ng/mL and in 40% of the patients with a PSA level of less than or equal to 3 ng/mL.

"Choline PET is a useful, functional method for detecting the site of recurrence for prostate cancer," Trampal said. "It can influence therapeutic strategy, providing information for selecting local or systemic therapy. We found a positive relationship between choline detection rate and serum PSA levels. The most positive results were in patients with PSA higher than 3 ng/mL."

RSNA attendee Dr. Hossein Jadvar, Ph.D., from the University of Southern California's Keck School of Medicine in Los Angeles, asked Trampal how his group verified their results because PSA decline alone may not be a reliable measurement since other pathologies can also cause a PSA drop. RSNA session comoderator Dr. Donald Podoloff added that biopsy was the only reliable way to confirm recurrence.

Trampal responded that his group was able to avoid biopsy in three patients with suspicion of local recurrence and successfully relied on the PET results along with the decline in PSA.