PET emerges as staging exam for cervical cancer

Preliminary study establishes PET/CT effectiveness for evaluating cancer after a negative CT findingSurgery has been the standard for cervical cancer staging for more than three decades, despite leading to complications, especially when followed by radiation therapy. Evidence continues to accumulate, however, indicating that PET studies may be up to the pretreatment challenge presented by the second leading cause of cancer mortality in women worldwide.

"Since the first reports of FDG-PET in patients with cervical cancer were published 10 years ago, the role of functional imaging in this disease has rapidly expanded," said Dr. Michael Gold, chair of the ongoing Gynecologic Oncology Group (GOG 233/ACRIN 6671) study on the utility of cervical cancer treatment planning with PET/CT and MRI (J Natl Compr Canc Netw 2008;6[1]:37-45).

Gold's team at the University of Oklahoma Health Sciences Center in Oklahoma City compared progression-free survival and overall survival in patients with locally advanced cervical cancer. One group underwent pretreatment imaging of the para-aortic lymph nodes, while the other had surgical sampling.

The investigators found that patients in the radiographic group had better baseline performance status and smaller tumor size compared with the surgical group. Subjects in the latter cohort, however, had better progression-free and overall survival rates. Gold's team acknowledged that PET's performance in this study may have been limited by the technology available between 1997 and 2000 (Cancer 2008;112[9]:1954-1963).

Investigators are tweaking how PET is used in this patient population. Dr. Yusuf Yildirim and colleagues at the Aegean Obstetrics and Gynecology Training and Research Hospital in Izmir, Turkey, found PET/CT to be an effective imaging technique for locally advanced cervical cancer when CT findings alone were negative. In their study, PET/CT turned in an accuracy of 75%, sensitivity of 50%, and specificity of 83.3% (Gynecol Oncol 2008; 108[1]:154-159). Yildirim's group used MRI and PET/CT in cervical cancer patients and found the latter modality to be the superior one.

"In our ongoing study, we identified nine patients who had negative results for para-aortic lymphadenopathy at MRI and subsequently proved to be positive at PET/CT. Positive findings at PET/CT were confirmed by extraperitoneal para-aortic lymphadenectomy," he said.

Dr. Farrokh Dehdashti, a professor of radiology at Washington University, and colleagues had similar good results with copper-60-labeled diacetylbis (Cu-60-ATSM-PET) for assessing tumor hypoxia, which is an early indicator of poor prognosis. They noted that radiotracer uptake was inversely related to progression-free survival and cause-specific survival (J Nucl Med 2008;49[2]:201-205).

The last word in PET for cervical cancer is most likely to come from the GOG/ ACRIN trial, which started enrolling patients in 2007 and has an accrual goal of 325 patients. Gold told Diagnostic Imaging that he envisions PET/CT serving as a triage tool, helping clinicians tailor treatment protocols.

"We've seen that microscopically positive nodes are not always detected with PET," he said. "But we've also seen that node-negative results on CT and PET can double survival. The biggest benefit is that when PET scans are completely negative, the likelihood of para-aortic metastases is close to zero."