LOCAL EXCISION OF PANCREATIC TUMOURS

Small, relatively benign types of tumours (usually functioning neuroendocrine tumours) may be amenable to local excision, avoiding sacrifice of healthy, functional pancreatic tissue. Local excision can only safely be done if the tumour is not close to the main pancreatic duct. When performing a local excision, it is essential to use magnification and intra-operative U/S, as well as extremely delicate dissection, to try to minimise the risk of injury to pancreatic ducts and to avoid leaving behind devascularised pancreatic tissue that could result in post-op pancreatitis or pancreatic fistulas.

Pancreatic tumours

The pancreas comprises two distinct components, the exocrine component and the endocrine component.

The exocrine component is responsible for producing and secreting enzymes that digest the food, breaking down complex molecules to their component amino acids, fatty acids, sugars etc. Components are absorbed from the gut into the blood and taken to the liver for conversion into complex human molecules. Pancreatic enzymes are secreted into the pancreatic ducts in an inactive form and, normally, only become activated after they enter the duodenum.

The endocrine cells produce hormones that are secreted directly into the blood and exert their chemical effects at sites remote from the pancreas. Insulin is the hormone known to most people, but there are numerous other hormones produced in the endocrine cells of the pancreas.

Tumours of the pancreas can arise from either the exocrine or the endocrine components. The biological behaviour of the tumours of the endocrine part is generally, although not always, much less aggressive than the tumours arising from the exocrine component.

Most pancreatic tumours are solid, but some are cystic. Cystic tumours have to be distinguished from simple cysts and pseudocysts.

Secondary (metastatic) cancers do occasionally occur in the pancreas too.

A simple pancreatic cyst is a collection of fluid surrounded by a layer of epithelial cells and supporting connective tissue in the pancreas. These may be associated with diseases such as polycystic kidney and liver disease and von Hippel-Lindau disease. This genetically inherited disorder may simultaneously affect the pancreas and other organs.

Pancreatic pseudocysts are localised collections of fluid and necrotic tissue surrounded by inflammatory fibrous tissue that forms after acute pancreatitis, pancreatic trauma or as a result of rupture of pancreatic ductules in chronic pancreatitis. By definition, pseudocysts do not have an epithelial lining. Pseudocysts are capable of compressing or eroding adjacent organs and blood vessels, so may need to be drained or excised to prevent serious complications.

Cystic pancreatic tumours may either be benign (cystadenomas) or malignant (cystadenocarcinomas).

Serous cystadenomas contain clear, watery fluid and are always benign, so, if they can be diagnosed with confidence, they do not need to be removed unless they are responsible for severe symptoms.

Mucinous cystic tumours contain mucoid fluid and may be benign or malignant. Benign ones can change, over time, to become malignant ones. Mucinous cystadenomas and cystadenocarcinomas contain tissue resembling ovarian stromal tissue, and the vast majority of these tumours occur in females, usually middle-aged females. They typically occur in the body and tail of the pancreas.

A very rare type of pancreatic tumour is known as solid pseudopapillary epithelial neoplasm (SPEN), and also has age and gender predisposition. They make up 1 to 2% of exocrine pancreatic lesions. Other names used for these tumours are solid pseudopapillary tumour (SPT) of the pancreas, solid pseudopapillary neoplasm (SPN), papillary cystic neoplasm of the pancreas, Hamoudi tumour, or Gruber-Frantz tumour. These are low grade with low malignant potential (10% to 15% of the cases are malignant), are commonly seen in young and adolescent females and rarely affect men. Accurate diagnosis of SPEN is of utmost importance since it has a low malignant potential. With prompt diagnosis and surgery, the patients could have a long life expectancy, including possible cure.

An increasingly frequently diagnosed type of mucinous cystic tumour is known as IPMN (intraductal papillary mucinous neoplasia). Microscopically, IPMN appears as tiny papillary (frond-like) growths in the pancreatic ducts, and these can be multiple. They secrete abundant mucus that distends the ducts. When these develop inside side branches of the central duct, the side ducts dilate to look like cysts that communicate with the main ducts. When they grow in the main ducts, they distend the main pancreatic ducts, either segmentally or along the entire length of the duct. Sometimes, with this dilatation of the duct, the sphincter of Oddi and papilla (where the duct opens into the duodenum) become patulous so that abundant mucus continuously discharges into the duodenum. These papillary micro tumours can progress to malignant pancreatic ductal adenocarcinoma.

Pancreatic ductal adenocarcinoma is the most common cancer that develops in the pancreas. Pancreatic ductal adenocarcinoma (PDAC) is generally a very aggressive type of cancer. PDAC has a poor prognosis because of its biological, behavioural patterns. This type of adenocarcinoma is often only diagnosed when it has invaded into adjacent structures or metastasised to lymph nodes, the liver, the peritoneum lining the abdomen or other more distant organs.

PDAC is often associated with a microscopic precancerous lesion called pancreatic intraepithelial neoplasia, PanIN. PanIN is the premalignant form from which invasive ductal adenocarcinoma develops. If it were possible to diagnose pancreatic intraepithelial neoplasia before it becomes invasive, the chances of curative treatment would be considerably better. Still, at this stage, this is very rarely, if ever, possible. We can, however, try to identify people who are at increased risk, and we can try to raise awareness so that early symptoms are not neglected. People who have or are related to people known to have inherited genetic conditions such as BRCA mutations and HNPCC (Lynch Syndrome) are at increased risk of developing PDAC and can be screened. People suffering from chronic pancreatitis are also at increased risk, and clinicians caring for these patients should be particularly aware of this and consider testing them, especially when they develop new-onset diabetes or other new symptoms. Other people who are at increased risk of PDAC are obese people and chronic smokers.

Early symptoms of PDAC may be new-onset diabetes mellitus, unexplained weight loss and non-specific upper abdominal or back pain, especially if it is in the lower thoracic or upper lumbar regions. Jaundice develops when a tumour invades and obstructs the primary bile duct. This may develop early if the tumour arises very close to the bile duct, but if the tumour arises further away from the duct, it may only be a late complication of advanced disease.

Unfortunately, there are no simple, inexpensive screening tests for pancreatic cancers. The sensitive tests currently available are contrast-enhanced CT and MRI scans of the abdomen and endoscopic ultrasound, which all need to be performed and interpreted by highly-trained specialists.

Endoscopic U/S involves inserting an endoscope with an attached Ultrasound probe through the mouth into the stomach and visualising the pancreas through the posterior wall of the stomach with the ultrasound. In addition to visualising the pancreas very well, it allows accurately passing a biopsy needle into any suspicious lesions to obtain aspirates for cytological assessment by a specialist pathologist.

DR GRAHAM STAPLETON

Dr Graham Stapleton is registered with the Health Professions Council of South Africa as a General Surgeon.

He specialises in liver and pancreatic surgery, with particular emphasis on removal of tumours of the liver and pancreas as well as other gastrointestinal cancers. He also supervises palliative treatments such as endoscopic and percutaneous stenting of obstructed bile ducts for those patients whose cancers are advanced and not resectable.

+27 (0) 21-6716181

+27 (0)82-569-4427

1406 Netcare Christian Barnard Memorial Hospital
Cnr DF Malan Street & Rua Bartholemeu Dias Plain
Foreshore, Cape Town, 8001