[Positron emission tomography (PET) for diagnosis and monitoring of treatment for urological tumors]. / Positronenemissionstomographie (PET) zur Diagnostik und zum Therapiemonitoring bei urologischen Tumoren.

Positron emission tomography (PET) using ((18)F)2-fluoro-D-2-desoxyglucose (FDG) has been shown to be a highly sensitive and specific imaging modality in the diagnosis of primary and recurrent tumors and in the control of therapies in numerous non-urologic cancers. It was the aim of this review to validate the significance of PET as a diagnostic tool in malignant tumors of the urogenital tract. A systematic review of the current literature concerning the role of PET for malignant tumors of the kidney, testicles, prostate, and bladder was carried out. The role of FDG PET for renal cell cancer can be seen in the detection of recurrences after definitive local therapy and metastases. The higher sensitivity of PET in comparison to other therapeutic modalities (CT, ultrasound, MRI) in recurrent and metastatic renal cell cancer suggests a supplemental role of this diagnostic procedure to complement other imaging modalities.The clinical value of PET is established for the identification of vital tumor tissue after chemotherapy of seminomatous germ cell tumors. This diagnostic method has little significance for primary tumor staging and diagnosis of non-seminomatous germ cell tumor because of the high probability of false-negative results in adult teratomas. FDG PET is not sensitive enough in the diagnosis of primary or recurrent tumors in prostate or bladder cancer. Also PET did not prove to be superior to conventional bone scintigram in the detection of mostly osteoblastic metastases in prostate cancer. The recent use of alternative tracers, which are partly not eliminated by urinary secretion (acetate, choline) has increased the sensitivity and specificity of PET also in this tumor entity so that further clinical investigations are needed to validate these technical modifications in their significance for this imaging modality. PET appears to be sufficiently evaluated only for the diagnostic follow-up of patients with seminomatous germ cell tumors after chemotherapy to regard it is the diagnostic tool of first choice. For all other tumors of the urogenital tract this proof is still awaited.

Monitoring isotretinoin therapy in thyroid cancer using 18F-FDG PET.

Treatment with isotretinoin (13-cis-retinoic acid, 13-cis-RA) is a recent additional option in advanced, otherwise intractable differentiated thyroid cancers. The aim of this study was to evaluate fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) in the prediction and the monitoring of response to 13-cis-RA therapy. Twenty-one patients with advanced differentiated thyroid cancers were investigated using 18F-FDG PET and iodine-131 whole-body scans before and 3, 6 and 9 months after initiation of 13-cis-RA therapy. After 9 months, 13-cis-RA treatment was discontinued and imaging procedures repeated 3 months later. Average 18F-FDG uptake (SUV) decreased significantly during 13-cis-RA therapy but subsequently increased in five of eight patients after withdrawal of 13-cis-RA. 18F-FDG uptake (SUV) 3 months after onset of 13-cis-RA therapy was significantly lower in patients who developed increased 131I uptake in their tumour sites than in patients with no subsequent increase in 131I uptake. There was no relationship between serum thyroglobulin level on the one hand and simultaneously measured 131I or 18F-FDG uptake on the other hand. There was a tendency towards lower 18F-FDG uptake in tumour manifestations with a better outcome. Therefore, 18F-FDG PET at 3 months after the start of treatment promises to differentiate between those patients who will eventually benefit from 13-cis-RA and those who will not. In conclusion, these data indicate that 18F-FDG PET is a useful tool for the evaluation and monitoring of adjuvant therapy with 13-cis-RA in thyroid cancer.