18Fluorodeoxyglucose-positron emission tomography in the management of patients with suspected pancreatic cancer

Abstract

Objective: To assess the accuracy and clinical impact of 18fluorodeoxyglucose-positron emission tomography (18FDG-PET) on the management of patients with suspected primary or recurrent pancreatic adenocarcinoma, and to assess the utility of 18FDG-PET in grading tumor response to neoadjuvant chemoradiation.

Summary background data: The diagnosis, staging, and treatment of pancreatic cancer remain difficult. Small primary tumors and hepatic metastases are often not well visualized by computed tomographic scanning (CT), resulting in a high incidence of nontherapeutic celiotomy and the frequent need for "blind resection." In addition, the distinction between local recurrence and nonspecific postoperative changes after resection can be difficult to ascertain on standard anatomic imaging. 18FDG-PET is a new imaging technique that takes advantage of increased glucose metabolism by tumor cells and may improve the diagnostic accuracy of preoperative studies for pancreatic adenocarcinoma.

Methods: Eighty-one 18FDG-PET scans were obtained in 70 patients undergoing evaluation for suspected primary or recurrent pancreatic adenocarcinoma. Of this group, 65 underwent evaluation for suspected primary pancreatic cancer. Nine patients underwent 18FDG-PET imaging before and after neoadjuvant chemoradiation, and in eight patients 18FDG-PET scans were performed for possible recurrent adenocarcinoma after resection. The 18FDG-PET images were analyzed visually and semiquantitatively using the standard uptake ratio (SUR). The sensitivity and specificity of 18FDG-PET and CT were determined for evaluation of the preoperative diagnosis of primary pancreatic carcinoma, and the impact of 18FDG-PET on patient management was retrospectively assessed.

Results: Among the 65 patients evaluated for primary tumor, 52 had proven pancreatic adenocarcinoma and 13 had benign lesions. 18FDG-PET had a higher sensitivity and specificity than CT in correctly diagnosing pancreatic carcinoma (92% and 85% vs. 65% and 62%). Eighteen patients (28%) had indeterminate or unrecognized pancreatic masses on CT clarified with 18FDG-PET. Seven patients (11%) had indeterminate or unrecognized metastatic disease clarified with 18FDG-PET. Overall, 18FDG-PET suggested potential alterations in clinical management in 28/65 patients (43%) with suspected primary pancreatic adenocarcinoma. Of the nine patients undergoing 18FDG-PET imaging before and after neoadjuvant chemoradiation, four had evidence of tumor regression by PET, three showed stable disease, and two showed tumor progression. CT was unable to detect any response to neoadjuvant therapy in this group. Eight patients had 18FDG-PET scans to evaluate suspected recurrent disease after resection. Four were noted to have new regions of 18FDG-uptake in the resection bed; four had evidence of new hepatic metastases. All proved to have metastatic pancreatic adenocarcinoma.

Conclusions: These data confirm that 18FDG-PET is useful in the evaluation of patients with suspected primary or recurrent pancreatic carcinoma. 18FDG-PET is more sensitive and specific than CT in the detection of small primary tumors and in the clarification of hepatic and distant metastases. 18FDG-PET was also of benefit in assessing response to neoadjuvant chemoradiation. Although 18FDG-PET cannot replace CT in defining local tumor resectability, the application of 18FDG-PET in addition to CT may alter clinical management in a significant fraction of patients with suspected pancreatic cancer.

Figure 1. ¹⁸FDG-PET documentation of CT-occult primary pancreatic ductal adenocarcinoma. The patient had obstructive jaundice and distal common bile duct stricture on endoscopic retrograde cholangiopancreatography. Helical CT failed to demonstrate a low-attenuation mass in the pancreatic head. ¹⁸FDG-PET demonstrated a focus of increased uptake in the region of the pancreatic head (SUR = 4.3). Pancreaticoduodenectomy was performed with histologic confirmation of a 1.2-cm pancreatic ductal adenocarcinoma. (A) Transverse reconstruction of ¹⁸FDG-PET demonstrating pancreatic head lesion (arrow). (B) Coronal view. (C) Sagittal view. (D) CT scan at the level of the tumor, demonstrating failure to detect the primary lesion.

Figure 2. ¹⁸FDG-PET documentation of CT-occult metastatic disease. The patient had obstructive jaundice. CT demonstrated a potentially resectable primary lesion in the pancreatic head, with an indeterminate subcentimeter lesion in the right lobe of the liver (A, arrow). ¹⁸FDG-PET demonstrated multiple CT-occult hepatic metastases (B), as well as unsuspected skeletal metastases in rib (C, arrow) and pelvis (D).

Figure 3. Assessment of response to chemoradiation using ¹⁸FDG-PET. Three representative examples of patients with biopsy-documented pancreatic ductal adenocarcinoma assessed by ¹⁸FDG-PET before (left panels) and after (right panels) neoadjuvant chemoradiation. In all three patients, CT showed no change in measurable tumor diameter. (A) Patient with treatment response documented by ¹⁸FDG-PET (pretreatment SUR = 3.0, posttreatment SUR = 0.0); note physiologic uptake of ¹⁸FDG in stomach anteriorly and in kidneys bilaterally. The resected specimen demonstrated grade 2A treatment effect (30% necrosis). (B) Patient with stable disease (<50% reduction in SUR) documented by ¹⁸FDG-PET (pretreatment SUR = 3.8, posttreatment SUR = 3.2). Resected specimen showed grade 1 treatment effect (<10% tumor necrosis). (C) Patient with progressive disease documented by ¹⁸FDG-PET (pretreatment SUR = 3.5, posttreatment SUR = 5.6). Disease was unresectable at laparotomy because of local tumor extension.