Because pancreatic cancer is usually silent until it is advanced, imaging has to do two jobs at once: find the tumour and decide whether it can be removed. The two jobs are related, because the same scan that shows the mass also shows whether it has invaded the vessels that would make resection impossible.
CT
The modality of choice for both diagnosis and staging is CT. Its overall sensitivity for pancreatic cancer is between 88 and 97%, but for lesions smaller than 2 cm it falls to 77%. CT is performed with intravenous and oral contrast agent, and it is used to:
- detect a mass in the pancreas;
- detect invasion of vascular structures such as the coeliac axis and the superior mesenteric artery, which is the main factor affecting the decision to resect;
- detect metastasis to other organs, such as the liver and peritoneum.
The CT criteria for the unresectability of a pancreatic tumour are:
- distant metastasis, such as to the liver or peritoneum;
- encasement of the coeliac axis or the superior mesenteric artery, and/or
- occlusion of the portal vein or the superior mesenteric vein.
EUS
The most accurate single test for the diagnosis of pancreatic cancer is EUS (endoscopic ultrasound), which images the pancreas from the stomach and the duodenum. Several studies show that EUS is more sensitive than CT for detecting pancreatic cancer, and in particular for tumours smaller than 3 cm, for which it outperforms both CT and MRI. Even so, MRI and CT remain necessary for detecting metastatic disease, for staging and for the assessment of resectability.
Confirming the diagnosis
When the tumour is unresectable, the diagnosis is confirmed by FNA (fine-needle aspiration) guided by CT or EUS, which obtains cells without the need for an operation. ERCP is no longer used as a diagnostic tool for pancreatic cancer, but it still has a role in palliative treatment, placing a stent in the biliary tract of patients whose tumour obstructs it.
No tumour-specific blood marker exists for pancreatic cancer. CA 19-9 is often raised, but it lacks specificity, so it is used mainly to follow known disease rather than to make the initial diagnosis.
Once the diagnosis is established, the decisive question is the same one the scans were asked to answer: can the tumour be completely removed? That question determines everything that follows in management.