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A small phase 2 study suggests that 17-fluorodeoxyglucose positron emission tomography ( FDG-PET ) may help identify occult masses after orchiectomy for stage 1 seminoma, said researchers here at the 2010 Genitourinary Cancers Symposium (ASCO-GU).

Current treatment standards for stage 1 seminoma call for adjuvant radiotherapy, adjuvant chemotherapy, or surveillance after orchiectomy. Because all 3 options offer cure rates of 90% to 100%, avoiding unnecessary treatment and the associated toxicity has become a priority for clinicians and researchers as well as for patients.

Computed tomography ( CT ) is often used to identify metastases in the pelvis, abdomen, and thorax, but a small percentage of patients experience relapse despite negative CT findings. FDG-PET has already been shown to identify residual masses after chemotherapy in advanced seminoma, prompting researchers to investigate the technique in less-advanced disease.

Yohan Loriot, MD, Institut Gustave Roussy, Villejuif, France, presented the findings here on March 7.

Dr. Loriot and colleagues performed an FDG-PET scan on 56 patients with stage 1 seminoma after orchiectomy and a negative CT scan of the pelvis, abdomen, and thorax. Patients were scanned between March 2004 and June 2008 and followed for a mean of 40 months.

Five of the patients had a positive FDG-PET, all with abnormalities in the retroperitoneum. All of these positive patients were treated with immediate chemotherapy. One patient had a doubtful FDG-PET, relapsed, and was also treated with adjuvant chemotherapy. None of the patients showed any further signs of relapse.

Of the 50 FDG-PET-negative patients, 7 requested adjuvant chemotherapy and 2 requested adjuvant radiotherapy. None of the 9 treated patients relapsed. Of the remaining 41 FDG-PET-negative patients, 5 relapsed with tumours in the retroperitoneum at 6, 8, 10, 16, and 18 months. One of the 5 was given radiotherapy, and the other 4 had chemotherapy; all remained disease free throughout the study period.

The 2-year relapse rate for FDG-PET-negative patients who did not request adjuvant treatment was 12.29%. With a median follow up of 40 months, the survival rate was 100%.

Researchers concluded that FDG-PET could help most postorchiectomy patients with stage 1 seminoma avoid unnecessary adjuvant treatment and the associated toxicities. Although a negative scan does not offer 100% assurance that the patient is free from occult metastases, FDG-PET was able to identify 55% (6 of 11) of patients with a disseminated seminoma that was not detected by conventional CT scan.

Source: ASCO

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