Accuracy of PET/CT in lymph node staging in patients with early-stage cervical cancer

Uterine cervical carcinoma is estimated to be the second most frequently diagnosed cancer in women and is a common cause of death in the female population. Although not included in FIGO clinical staging, the pelvic and paraaortic lymph node status is an important prognostic factor in early-stage cervical cancer and may alter patient management.

The purpose of the present study was to perspectively determinate the accuracy of PET/CT in lymph node staging in patients with early-stage cervical cancer, with histopathologic results as the reference standard. The study included 47 consecutive women with early-stage cervical cancer scheduled for radical hysterectomy with pelvic lymph node dissection. Before surgery, all patients underwent FDG PET/CT. PET/CT findings were interpreted and compared with histopathologic results. The overall node-based sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of PET/CT were 72%, 99.7%, 81%, 99.5% and 99.3%, respectively. Corresponding values for PET/CT-based diagnosis of lymph nodes larger than 0.5 cm in diameter were 100%, 99.6%, 81%, 100% and  99.6%, respectively. This improved PET/CT performace is due to the spatial resolution of PET component, which is in the range of 0.4-0.6 cm. Such a still limited spatial resolution makes the presence of metastasis in small lymph nodes hardly detectable, even at PET/CT, as confirmed by false-negative lymph nodes smaller than 0.5 cm in diameter reported in this series. The overall patient-based sensitivity sensitivity, specificity, PPV, NPV, and accuracy of PET/CT were 73%, 97%, 92%, 89% and 89%, respectively.

In contrast to CT and MR imaging, which yield morphological information, FDG PET may noninvasively detect primary and metastatic tumor types on the basis of the increased glucose metabolism of malignant tissue. With PET/CT, in fact, the capability to differentiate malignant nodes, presenting as foci with high FDG uptake at PET, is not compromised by the use of morphological criteria.

PET/CT proved to be valuable for pre-operative lymph node staging in patients with early-stage cervical cancer, with greater than 0.5 cm short-axis diameter, being the size threshold for accurate depiction of metastatic nodes. If the results of forthcoming studies of lymph node metastasis in cervical cancer will confirm these findings, integrated PET/CT may become an alternative to CT and MR imaging for lymph node staging in patients with this cancer.

Reference:

Sirono S et al.: "Lymph Node Metastasis in Patients with Clinical Early-Stage Cervical Cancer: Detection with Integrated FDG PET/CT", Radiology. 2005 Nov 22; [Epub ahead of print]

Maria Picchio

Department of Nuclear Medicine, Institute H S. Raffaele, Milan, Italy