An Introduction to the Pancreas and its Cancer(s)

Given that the four-year PhD I am about to embark on is being partly funded by Cancer Research UK (CRUK), why not start with a short video they have put together containing ten things about that pancreatic cancer that you may (not) have known:

Firstly, is there anything more to its anatomy than “being a small organ in the abdomen”? Why yes, funny you should ask. The pancreas reaches up to 15 cm in length in humans and is a J-shaped structure, apparently a bit like a hockey stick. The organ is not symmetric, rather it is made of a head (left), body (middle) and tail (right), as shown below. In the head the main pancreatic duct merges with the common bile duct before they join into the duodenum, where food is further digested after it leaves the stomach.

Screen Shot 2015-09-04 at 22.08.59

Cartoon illustration of a human pancreas – copied directly from Hezel et al, 2006

As is often the case in biology – and this applies from the level of individual proteins to a whole organism – there is an intricate relationship between structure and function. The pancreas has two main functions: firstly, it contains endocrine cells that produce hormones, such as insulin, to regulate glucose balance (or homeostasis). Secondly, it contains exocrine cells, which make up the majority of the organ, that produce enzymes to aid food digestion. These two categories of cells therefore work together and coordinate the body’s metabolic response to food consumption.

Not all animals have pancreases as complex as those found in mammals since they have evolved over time. Worms, for instance, have some specialised gut cells that produce a substance similar to insulin. Ancient sharks and some fish contain organs in which the exo- and endocrine cells are found together. Fruit flies astonishingly produce insulin in their brains and, in particular, those cells develop from a completely different tissue in the embryo – called the ectoderm – than in other animals, where the pancreas stems from the endoderm. In amphibians and mammals the anatomy becomes more complex with characteristic “islets” of endocrine cells. (See Stanger & Hebrok, 2013 for more details.)

Since I am the daughter of two doctors I am usually interested in the pathological side of human biology. What sort of diseases befall the pancreas? Possibly the first that comes to mind is (type I, auto-immune type) diabetes in which the pancreas fails to make enough insulin because the body is attacking its own beta cells that normally produce insulin. Other than that the pancreas can of course become inflamed like any other organ and this is known as pancreatitis. It is caused, among other things, by high doses of alcohol. Lastly, the pancreas can become cancerous.

Although there are a few different types of pancreatic cancer the focus will lie on pancreatic ductal adenocarcinoma (PDAC) since it is both the most frequent and also the best understood type. It is one of the deadliest types of cancer because it often goes unnoticed until the tumour has disseminated (or metastasised) in the body – fewer than 10% of people who are diagnosed survive for longer than five years.

Therefore it is important to find out more about PDAC. But for the moment there is a lot we do know, decades of hard work that are often frustratingly glossed over. For instance, the genetic mutations that start and maintain PDACs are well known. Among them are activating mutations in a famous oncogene – a gene whose overactivation contributes to cell proliferation and cancer – called KRAS, and deletions of tumour suppressors – those genes/proteins that act as checks and balances and stop cells from overproliferating – such as p16 and p53. Moreover, it is well known when these mutations occur during the development of the cancer. The following image shows how some PDACs form: from healthy tissue to slightly abnormal tissue until it invades into the rest of the body.

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Histology of normal (left), dysplastic (middle) and malignant (right) pancreatic tissue – copied directly from Bardeesy & DePinho, 2002

As for treatment, the most effective method, if successful, is surgery. However, this often involves removing the head of the pancreas as well as parts of the duodenum and this, in turn, means that the stomach has to be surgically joined directly to subsequent parts of the digestive tract, making it a complex procedure. In addition, patients receive radio- and/or chemotherapy, which “targets” most proliferating cells. Targeted therapies that are specific to the cancer cells, as opposed to healthily dividing cells, are, as far as I am aware, not particularly established yet for pancreatic cancer.

For surgery to be effective the cancer needs to be detected at earlier stages. In other words, better diagnosis procedures need to be developed. Recently, two papers attracted some attention because they uncovered methods that could potentially make diagnoses easier using either blood (Melo et al, 2015) or urine (Radon et al, 2015) samples. However, as CRUK rightly point out, these techniques need to be refined for them to be able to tell true cancers from chronic pancreas infections.

And on that cheery note… Next time you can look forward to learning a bit more about how PDAC is studied in the lab and pancreatic anatomy in slightly more detail.

References:

Bardeesy N, DePinho RA (2002) Pancreatic cancer biology and genetics. Nat Rev Cancer 2: 897-909

Hezel AF, Kimmelman AC, Stanger BZ, Bardeesy N, DePinho RA (2006) Genetics and biology of pancreatic ductal adenocarcinoma. Genes & Development 20: 1218-1249

Melo SA, Luecke LB, Kahlert C, Fernandez AF, Gammon ST, Kaye J, LeBleu VS, Mittendorf EA, Weitz J, Rahbari N, Reissfelder C, Pilarsky C, Fraga MF, Piwnica-Worms D, Kalluri R (2015) Glypican-1 identifies cancer exosomes and detects early pancreatic cancer. Nature 523: 177-182

Radon TP, Massat NJ, Jones R, Alrawashdeh W, Dumartin L, Ennis D, Duffy SW, Kocher HM, Pereira SP, Guarner  L, Murta-Nascimento C, Real FX, Malats N, Neoptolemos J, Costello E, Greenhalf W, Lemoine NR, Crnogorac-Jurcevic T (2015) Identification of a Three-Biomarker Panel in Urine for Early Detection of Pancreatic Adenocarcinoma. Clinical Cancer Research 21: 3512-3521

Stanger BZ, Hebrok M (2013) Control of Cell Identity in Pancreas Development and Regeneration. Gastroenterology 144: 1170-1179

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One thought on “An Introduction to the Pancreas and its Cancer(s)

  1. Pingback: A bit more pancreas | Gotta Love Cells

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