Meditations of an oncology geek

Why is Pancreatic Cancer hard to treat?

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This week marks another question from Peter Borak of San Francisco, CA:

Why are some cancers fatal and other cancers easy to treat?

This question seems quite timely given the untimely death of Apple guru Steve Jobs this week from Pancreatic Cancer.

The cancers that are easily detectable tend to be the most treatable. For instance, skin cancer is frequently curable. Like most cancers, cancers of the skin take years or even decades to develop. But, pre-cancerous lesions (funny-looking moles, for instance) are easily spotted and removed.

This stands in stark contrast to, say, cancer of the pancreas. Pancreatic cancer has a mean survival time of less than 6 months from diagnosis. The first reason why is because symptoms usually do not present until late disease. Severe abdominal pain and unexplained weakness are often conflated with other more common illnesses, like indigestion and the flu.

However, Jobs actually caught his cancer fairly early (1). He had a history of gastrointestinal problems and received scans as part of his regular physical examinations. These are expensive and uncommon to have as part of routine physicals, as it is very difficult to scan the area surrounding the pancreas.

This brings me to the second reason why some cancers are harder to treat than others: propensity to metastasize and spread. Pancreatic cancers often spread very quickly and colonize other vital organs nearby, like the liver. Once cancers begin to spread, it’s very, VERY hard to eradicate. I like to use the analogy of a weed’s spores seeding a garden. Once the weeds start to spread, it’s an uphill battle. The weeds will grow and out-compete everything else in the garden without extreme care and effort, and will consistently spring back. A tumor can shed millions of tumor cells into blood circulation per day, and any of those have the potential to wreak havoc on vital organs. Tumor cells also have the ability to remain dormant for years in distant soils of other organs, evading chemotherapy. When cancer is in this state, known as “micrometastasis” it has seeded vital organs and lying dormant, undetectable by modern medal scanning.

The third main reason why some cancers are harder to treat then others is somewhat related to the first point: surgical removal can be very difficult. I will again refer to pancreatic cancer. The pancreas is an organ surrounded by many other vital organs, making surgical removal of tumors an extremely delicate procedure. Jobs underwent the whipple procedure (2) which

“consists of the en bloc removal of the distal segment (antrum) of the stomach; the first and second portions of the duodenum; the head of the pancreas; the common bile duct; and the gallbladder.
The basic concept behind the pancreaticoduodenectomy is that the head of the pancreas and the duodenum share the same arterial blood supply (the gastroduodenal artery). These arteries run through the head of the pancreas, so that both organs must be removed if the single blood supply is severed. If only the head of the pancreas were removed it would compromise blood flow to the duodenum, resulting in tissue necrosis.”

From a logistics standpoint, it might be easier to build a ship in a bottle – blindfolded – than to successfully remove tumors from the pancreas.

Jobs had been notoriously secretive about his illness, but it became known that in 2009 Jobs had a liver transplant. The cancer research community collectively raised an eyebrow. The liver is one of the first places that pancreatic cancer metastasizes to. Given Jobs’s previous declaration that he was cured of his disease, we watched with a somber eye.

So, in general, the easier the cancer is to detect early, the greater the survival. The more difficult to detect cancers, as well as those more difficult for surgical intervention, are the ones that have higher fatality rates. As for Jobs, there is some controversy regarding the direction he took in battling his cancer, including the use of alternate therapies, like the Gonzalez procedure (3) that had been previously proven to be ineffective and even dangerous by peer-reviewed scientific studies. However, that is a discussion for another time.



Written by Ryon

October 9th, 2011 at 12:37 pm

Posted in Science Blog

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