When squamous cell carcinoma is detected in pancreatic tumors, there are two possibilities: primary pancreatic cancer or pancreatic metastasis. Adenocarcinoma accounts for about 75–81% of primary pancreatic cancers, and pure squamous cell carcinoma is very rare (10–13). According to a 1992 report from Japan, squamous cell carcinoma accounted for only 0.7% of 1,300 cases of pancreatic cancer (14). Normally, squamous epithelium does not exist in the pancreas, but inflammation from conditions such as pancreatitis can lead to squamous epithelialization of ductal columnar cells.
Squamous cell carcinoma of the pancreas is thus thought to arise from squamous metaplasia of ductal columnar cells secondary to chronic inflammation (15). However, metastases to the pancreas account for less than 2% of all pancreatic malignancies (9). Metastases from kidney, lung, breast, colon, and skin (melanoma) cancers, along with sarcomas, frequently involve the pancreas (7). However, metastases even from squamous cell carcinoma of the lung, which is the most frequent primary cancer to metastasize to the pancreas, account for only 1.1% of cases (16). Thus, simultaneous primary and metastatic squamous cell carcinoma of the pancreas is rare. Of note, there are few metastases from a primary cancer of the esophagus to the pancreas; therefore, the advantages and disadvantages of resection remain unknown.
Resection for pancreatic metastases from renal cell or ovarian cancers and complete resection of metastases from any primary cancer have been reported to be beneficial in prolonging survival (8,9,16,17). Solitary pancreatic metastases tend to be resected, although our literature search only discovered 4 patients who underwent resection of pancreatic metastases from esophageal squamous cell carcinoma (18–20). Furthermore, resection of simultaneous metastases was reported for only one of the 4 cases (21).
A review of the surgical data of 5 reported cases (4 from the literature search plus our case), showed that every patient underwent distal pancreatectomy and was discharged without postoperative complications (Table 1) (18–21). Postoperative adjuvant 5-fluorouracil/cisplatin chemotherapy was administered to 3 patients and there was a report of no recurrence for up to 24 months (18). The lower thoracic esophagus was the site of the primary tumor in 3 cases. One case report did not provide the location of the primary tumor. All pancreatic metastases occurred in the pancreatic tail.
Blood drains from the cervical esophagus into the superior vena cava via the inferior thoracic vein, and blood drains from the upper or middle thoracic esophagus into the superior and inferior vena cava via the azygous and hemi azygous veins. On the other hand, blood draining from the lower thoracic esophagus and the abdominal esophagus flows into the portal system via the paraesophageal vein and the left and short gastric veins (22). Thus, esophageal carcinoma in the lower thoracic esophagus may be more prone to metastasize to the pancreas than esophageal squamous cell carcinomas located elsewhere, because drainage via the paraesophageal vein to the splenic vein is the predominant route of blood flow. The anatomy of the draining veins may also account for the frequency of pancreatic metastases to the pancreatic tail.
Squamous cell carcinomas discovered in the pancreas must be determined to be either a primary cancer or metastatic disease. The frequency of pancreatic metastases from squamous cell carcinoma is much higher than the frequency of primary squamous cell carcinoma of the pancreas; thus, it is generally reasonable to assume that a pancreatic tumor is a metastasis from squamous cell carcinoma of the esophagus (23). The histopathologic findings in our patient showed neoplastic changes in the esophageal mucosa, and also carcinoma in situ. These findings indicate that the primary tumor was located in the esophagus. Additionally, the histopathologic findings of the specimen from the pancreas showed that the tumor was not in contact with the main pancreatic duct and that there were no atypical findings seen in the main pancreatic duct. Both the esophageal and pancreatic tumors showed extensive venous invasion and similar histopathologic profiles. Given these data, we finally diagnosed the tumor in the pancreas as a pancreatic metastasis from esophageal cancer.
The preoperative confirmation that the tumor in the pancreas is a solitary metastasis, which leads to the possibility of a complete resection, is important, because resection of a solitary metastasis is associated with improved survival (8,9). In general, the differentiation between a pancreatic metastasis of esophageal cancer and a primary pancreatic cancer can be made by a preoperative EUS-FNA biopsy for tissue diagnosis (24,25). When a tumor is found in the pancreas concomitant with an esophageal squamous cell carcinoma that is located in the lower esophagus, the pancreatic tumor should be considered a metastasis. The confirmation of the diagnosis is essential for deciding on the treatment, and should be obtained from a preoperative diagnosis of specimens from EUS-FNA or from Positron emission tomography-computed tomography (PET-CT).
Thus far however, there have not been any published prospective or case-controlled clinical trials that compared the efficacy of resection with the nonoperative treatment of pancreatic metastases. The surgical mortality of pancreatic surgery has been shown to be less than 5% (9), and since the 5 patients in the published literature remain alive, surgery for patients with a solitary pancreatic metastasis from esophageal squamous cell carcinoma may improve outcomes and should be considered. However, the follow-up periods of the previous reports were short, and further observation of these patients is needed to determine the prognosis of such cases.