Clinical usefulness of dual-time FDG PET–CT in assessment of esophageal squamous cell carcinoma
Introduction
Esophageal cancer is a lethal malignant cancer with a poor prognosis. The 5-year survival rate for most cases diagnosed in the advanced stage is only 10–30% for resectable tumors and 5% for unresectable ones [1]. Information regarding tumor invasion depth, lymph node involvement, and distant metastasis is important in deciding the appropriate treatment for esophageal cancer. Accurate assessment of tumor extent and nodal involvement is essential for curative resection.
Various imaging tools, such as computed tomography (CT) scan and, endoscopic ultrasonography (EUS) are widely used in routine clinical practice. These imaging tool are useful for evaluating the extent of the disease but have limitations when determining lymph nodes metastasis [2], [3], [4]. In the past, computed tomography (CT) scanning was the major staging method, but recently, 2-[18F]fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET) scanning has become more widely used [5]. The FDG PET is used for diagnosis, initial staging, restaging, prediction, and monitoring of treatment response, surveillance, and prognostication in a variety of cancers [6], [7], [8]. However, FDG PET does not allow for the precise localization of landmarks, making it difficult to identify the foci of the increased FDG uptake [9]. The role of FDG PET in the detection of nodal metastasis is still controversial and its efficacy is far from ideal.
Integrated FDG PET–CT is a new functional and metabolic imaging tool. Many reports indicate that FDG PET–CT is more sensitive and specific in the diagnosis and staging of several types of malignancies than FDG PET [6], [10], [11]. However, FDG uptake is not tumor specific. Traditionally, a threshold for a single time point standardized uptake value (SUV) of 2.5–3.5 has been proposed as the optimal threshold for distinguishing between benign and malignant lesion in various literatures. Many researchers found that when SUV is measured, there is a correlation between the FDG uptake and time. In tumor, the uptake of FDG uptake continues to increase for several hours after FDG injection whereas such prolonged period of FDG uptake is rare in inflammatory/infectious or normal tissues. This may be related to the graded concentration of FDG in tumor cells, low glucose-6-phosphatase activity, and increase glucose uptake through glucose transporter in these cells [12], [13], [14], [15], [16], [17].
Therefore, recognition of these imaging pitfalls is an important step in patient assessment. Various cell types exhibit varying rates of FDG uptake. Dual-time-point scanning of FDG PET has been widely applied in many kinds of cancers. Most of them seem useful in differentiating between inflammation and malignancy because of the additional qualitative and quantitative information derived from these scans [12], [15], [16], [17]. Hence, the method has been routinely used in all FDG PET scans of our institute. However, poor discriminability of dual-time-point method has also been found in few studies. Nevertheless, the efficacy of such method for esophageal cancer is seldom reported or discussed in the literature. Thus, the purpose of current study is aimed to analyze the relation between findings of dual-time-point FDG PET–CT and clinical/pathological results of the primary tumor, lymph nodes and distant metastasis of the esophageal cancers retrospectively, and tries to discuss the potential use of dual-time-point method in such circumstance [12], [18], [19], [20], [21].
Section snippets
Patient population
Twenty-six patients (all men; age range, 42–72 years old; mean age, 60.4 years) who underwent preoperative FDG PET–CT scan and subsequent surgical resection of esophageal cancer between October 2009 and April 2010 in China Medical University Hospital were retrospectively included in this study. All patients histologically proved to have squamous cell carcinoma and had received esophageal resection and regional lymph nodes dissection (Table 1). Surgical pathology results were used to provide the
Primary tumor
The sensitivity of FDG PET–CT in detecting the primary tumor site with combination of early SUVmax ≧ 2.5 or RI ≧ 10% was 96.2%. It was statistically significantly higher than the other 3 criteria. The p value of Fisher's exact test was <0.0001 and it was statistically significant (Table 2).
Regional lymph nodes
The sensitivity of early SUVmax ≧ 2.5 alone was 30.0%, but it increased to 70% when combination of early SUVmax ≧ 2.5 or RI ≧ 10% was used. However, the p value was only 0.1181 and hence not significant. For the
Discussion
FDG PET–CT is widely used with cancer patients. Its role as a non-invasive imaging modality has been widely investigated but the exact SUVmax cutoff value for esophageal cancer remains controversial. To accurately distinguish malignant from benign lesion is challenging because FDG is taken up not only by tumor cells but by inflammatory cells as well [11], [20], [21], [22], [23].
Although the potential of dual-time FDG PET in evaluating various cancers has been reported, the diagnostic value of
Conclusion
The preliminary result of this study demonstrated that dual-time point FDG PET–CT had limited value in detection of primary tumor and loco-regional lymph node metastasis. For the distant metastasis, the sensitivity and specificity would be improved if RI ≧ 10% was used as a supplement criterion. Efforts should be made to improve the ability of the dual-time FDG PET–CT technique to assess primary tumor and loco-regional lymph nodes metastasis.
Acknowledgements
This study was supported by a grant from China Medical University Hospital (DMR-98-050 and DMR-98-052) and the Department of Health, Clinical Trial and Cancer Research Centers for Excellence, Taiwan (DOH100-TD-B-111-004 and DOH100-TD-C-111-005).
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