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Pancreas as a site of metastatic cancer
Introduction
The pancreas is a rare site of distant metastasis. In 1950 in an autopsy study, Abrams et al. were one of the first to highlight the pancreas as a potential site for metastatic spread. Overall, these metastatic lesions constitute only a minor portion (approximately 2%–5%) of all pancreatic neoplasms. , The most common sites of primary carcinoma for metastatic spread to the pancreas are renal cell carcinoma (∼50%) followed by colorectal cancer (∼10%). Still, a variety of different cancer sites have been described as a source of spread, such as melanoma, lung cancer, and gastric cancer. The majority of patients metastatic disease to the pancreas also have widespread systemic disease at the time of diagnosis and are not candidates for surgical resection.
Given the rarity of solitary pancreatic metastasis, surgical experience is mainly restricted to case series of limited size. Whereas pancreatectomy remains essential in the curative treatment of primary pancreatic cancer (see Chapter 62 ), the role of resection is less well understood for metastasis into the pancreas. Historically, resected pancreatic metastases were often misdiagnosed as primary cancers and were identified as metastatic disease by post-operative histologic assessment of the specimen. In 1972 Guttmann et al. presented one of the first cases of a renal cell metastases to the pancreas treated by total pancreatectomy. Similar to a later case series by Zgraggen et al., it was assumed that the disease was a primary pancreatic tumor before resection. , Still, over time a number of encouraging reports suggested potential oncologic benefits from pancreatic metastasectomy in selected patients. , ,
Clinical presentation and the challenge of diagnosis
Clinical presentation
Pancreatic metastasis are not necessarily associated with symptoms. The literature suggests that approximately 50% of patients are asymptomatic at the time of diagnosis. , , In symptomatic patients, the spectrum of symptoms is similar to clinical manifestations of primary pancreatic neoplasia. Abdominal pain, obstructive jaundice and gastric outlet obstruction or hemorrhage are commonly described. , , However, many patients present with incidental findings during the extent of disease work-up for the primary cancer or during disease surveillance after treatment of the primary disease.
Diagnosis
The major challenges for the diagnosis are, firstly, to distinguish metastasis from primary pancreatic cancer and then to exclude the presence of disseminated disease. Often a suspicious lesion detected on computed tomography (CT) is the first indication of a pancreatic metastasis (see Chapter 17 ). From a morphologic standpoint, metastases to the pancreas may display similar characteristics to a primary tumor. In that context, intravenous (IV) contrast protocols for axial imaging are essential to enable a description of vascularization patterns and already may hint to the primary source. Metastasis originating from hypovascular primaries (i.e., colon, gastric, or lung cancer) mostly occur as hypoattenuated lesions, metastasis from hypervascular cancers (i.e., renal cell, hepatocellular, or thyroid cancer) display increased vascularity on CT. This is of particular importance for metastases from renal cell carcinomas that display strong early enhancement at CT and MRI, a pattern that mirrors the hypervascularity of the primary tumor tissue ( Fig. 64.1 A–B).
Routine use of magnetic resonance imaging (MRI) is not mandatory but may help identify duct infiltration, indicating a primary originating from the pancreatic duct itself (see Chapter 17 ). Endoscopic ultrasound (EUS) with fine needle aspiration (FNA) is also a valuable diagnostic tool (see Chapter 22 ). Histologic analysis may be extended by specific immunohistochemistry for certain entities: that is, neuroendocrine tumor (Synaptophysin, Somatostatin), breast cancer (ER, PR, Her2/neu) or lung and thyroid cancer (TTF-1). Tumor markers such as carbohydrate antigen 19-9 (CA 19-9) or carcinoembryonic antigen (CEA) may be helpful laboratory parameters to discriminate a primary from a metastatic pancreatic lesion.
Some authors have recommended preoperative fluorodeoxyglucose–positron-emission tomography (FDG-PET), excluding the presence of extra pancreatic disease (see Fig. 64.1C–D ) (see Chapter 18 ). We believe that this is useful particularly if the patient has a colonic, renal, or melanoma primary. Metastasis from renal cell carcinoma may express somatostatin receptors and can show a similar uptake pattern as neuroendocrine tumors on OctreoScan scintigraphy.
The pattern of metastasis is of no less importance for surgical planning. Whereas the solitary lesion is reported to be the most common manifestation of metastasis to the pancreas (50%–75%), diffuse infiltration or multinodular disease may prevent a pancreas preserving surgical strategy and result in total pancreatectomy. ,
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