December 10, 2018Quiz
By OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30148457
Pancreatic cancer is the fourth leading cause of cancer 1) ___ in the United States. Approximately 32,?000 individuals in the USA and over 200,?000 individuals worldwide die from the disease each year. The incidence approximates the mortality rate, which reflects the poor prognosis of pancreatic cancer. Although there have been many advances in pancreatic cancer research, the 5-year survival rate for affected patients remains under 5%.
The aggressiveness that characterizes pancreatic cancer arises from multiple heterogeneous genetic changes that occur before the onset of clinical symptoms. Studies performed over the past decade have shed some light on the molecular and histological events that are associated with pancreatic carcinogenesis. Future progress in this area will hopefully lead to improved diagnostic tests, early detection, and new treatments for patients who suffer from this devastating disease. The accumulation of multiple nonrandom genetic changes over time is a hallmark of pancreatic cancer. Genetic abnormalities include alterations in chromosome or 2) ____ copy number, microsatellite instability, epigenetic silencing, intragenic point mutations, and gene overexpression secondary to increased transcription.
Pancreatic cancer arises when cells in the pancreas, a glandular organ behind the 3) ___, begin to multiply out of control and form a mass. These cancerous cells have the ability to invade other parts of the body. There are a number of types of pancreatic cancer. The most common, pancreatic adenocarcinoma, accounts for about 85% of cases, and the term pancreatic cancer is sometimes used to refer only to that type. These adenocarcinomas start within the part of the pancreas which makes digestive enzymes. Several other types of cancer, which collectively represent the majority of the non-adenocarcinomas, can also arise from these cells. One to two percent of cases of pancreatic cancer are neuroendocrine tumors, which arise from the hormone-producing 4) ___ of the pancreas. These are generally less aggressive than pancreatic adenocarcinoma. Signs and symptoms of the most common form of pancreatic cancer may include yellow skin, abdominal or back pain, unexplained 5)___ loss, light-colored stools, dark urine and loss of appetite. There are usually no symptoms in the disease's early stages, and symptoms that are specific enough to suggest pancreatic cancer typically do not develop until the disease has reached an advanced stage. By the time of diagnosis, pancreatic cancer has often spread to other parts of the body.
Pancreatic cancer rarely occurs before the age of 40, and more than half of cases of pancreatic adenocarcinoma occur in those over 70. Risk factors for pancreatic cancer include tobacco smoking, obesity, diabetes, and certain rare genetic conditions. About 25% of cases are linked to smoking, and 5-10% are linked to inherited genes. Pancreatic cancer is usually diagnosed by a combination of medical imaging techniques such as ultrasound or computed tomography, blood tests, and examination of tissue samples (biopsy). The disease is divided into stages, from early (stage I) to late (stage IV). Screening the general population has not been found to be effective. The risk of developing pancreatic cancer is lower among non-smokers, and people who maintain a healthy weight and limit their consumption of red or processed meat. A smoker's chance of developing the disease decreases if they stop 6) ___, and almost returns to that of the rest of the population after 20 years.
Pancreatic cancer can be treated with surgery, radiotherapy, chemotherapy, palliative care, or a combination of these. Treatment options are partly based on the cancer stage. Surgery is the only treatment that can cure pancreatic adenocarcinoma, and may also be done to improve quality of life without the potential for cure. Pain management and medications to improve digestion are sometimes needed. Early palliative care is recommended even for those receiving treatment that aims for a cure. The disease occurs most often in the 7) ___ world, where about 70% of the new cases in 2012 originated. Pancreatic adenocarcinoma typically has a very poor prognosis: after diagnosis, 25% of people survive one year and 5% live for five years. For cancers diagnosed early, the five-year survival rate rises to about 20%. Neuroendocrine cancers have better outcomes; at five years from diagnosis, 65% of those diagnosed are living, though survival varies considerably depending on the type of tumor.
The pancreas has multiple functions, served by the endocrine cells in the islets of Langerhans and the exocrine acinar cells. Pancreatic cancer may arise from any of these and disrupt any of their functions. The many types of pancreatic 8) ___ can be divided into two general groups. The vast majority of cases (about 95%) occur in the part of the pancreas which produces digestive enzymes, known as the exocrine component. There are several sub-types of exocrine pancreatic cancers, but their diagnosis and treatment have much in common. The small minority of cancers that arise in the hormone-producing (endocrine) tissue of the pancreas have different clinical characteristics and are called pancreatic neuroendocrine tumors, sometimes abbreviated as PanNETs. Both groups occur mainly (but not exclusively) in people over 40, and are slightly more common in men, but some rare sub-types mainly occur in women or children.
Pancreatic cancer can be difficult to diagnose. That's partly because the pancreas is located deep in the belly and is difficult to feel or examine, and partly because symptoms may develop gradually. A single standard diagnostic test for pancreatic cancer does not yet exist. So, if a person has symptoms that suggest pancreatic cancer, his or her doctor may use a variety of tests to make the diagnosis and to stage the cancer. The tests may include a number of different imaging tests (MRI, CT, PET, and ultrasound) as well as blood chemistry studies, biopsies, and more. The diagnostic tests the doctor orders may differ depending on whether he or she suspects an exocrine tumor or a pancreatic neuroendocrine tumor (PNET). While it is virtually impossible to tell what caused a specific person to develop pancreatic cancer, there are some important principles of cancer biology that can help us understand why pancreatic cancer develops, and large population-based studies help us understand the many risk factors for this disease.
Pancreatic cancer is fundamentally a disease caused by damage to the DNA. This damage is often referred to as mutations. These 9) ___ can be inherited from either parent, or they can be acquired as we age. With inherited mutations, there are two copies of each gene - one copy we inherit from our mother, the other copy we inherit from our father. Most individuals with an inherited cancer syndrome inherit one mutant copy (let us say from dad) and one intact (normal) copy (let us say from mom) of a cancer associated gene. As these individuals with an inherited cancer syndrome age, some of will sustain damage the good copy of the gene (the copy they got from mom) in a cell in their pancreas. That cell will then have two damaged copies of the gene (one inherited and one acquired during life), and, as a result, that cell in the pancreas will begin to grow abnormally and will eventually form a cancer. From this understanding it should be clear that not everyone with an inherited predisposition will get cancer. Instead, since individuals with an inherited cancer syndrome are born with only one good copy of the cancer associated gene, they are more likely to get cancer. The second way we can damage our DNA is with our behavior. For example, the carcinogens (cancer causing chemicals) in cigarette smoke can damage our DNA. If the carcinogens damage a key cancer-associated gene in a cell in the pancreas, then that cell may grow into a cancer. Simply put, don't smoke! The third way our DNA gets damaged is by chance. This is probably the least satisfying explanation, but it is true. Every cell in our body (and there are trillions of them!) contains two copies of each of the 23 chromosomes and these 46 chromosomes contain billions of base-pairs (letters) of DNA. Every time a cell divides it has to copy all of that DNA (so that it can make daughter cells with a full complement of DNA). The DNA copying machinery in cells is good, but is not perfect. Occasionally mistakes are made copying DNA. On one hand, this is good from the perspective of a population or species, because these mistakes allow for evolution to occur (if we copied our DNA perfectly we would not evolve!). On the other hand, if one of these chance mistakes in copying (DNA mutations) damages a key cancer-associated gene in a cell in the pancreas, then that cell may grow into a cancer.
To summarize, pancreatic cancer is caused by DNA mutations, and there are three ways that we can damage our DNA. We can be born with a DNA mutation inherited from our mother or father, we can do something, like smoking, that damages our DNA, or finally our DNA can be damaged by chance. The second way to answer the question about what causes pancreatic cancer is to ask what are the risk factors for pancreatic cancer? Some of the risk factors include: Cigarette smoking doubles the risk of pancreatic cancer. In fact, some scientists have estimated that one in four, or one in five cases of pancreatic cancer are caused by smoking cigarettes. Smoking is also associated with early age at diagnosis. Very importantly, the risk of pancreatic cancer drops close to normal in people who quit smoking. Simply put, 10) ___ smoking is the leading preventable cause of pancreatic cancer.
Sources: http://www.mcancer.org/news/archive/what-makes-pancreatic-cancer-so-aggressive-new-study-sheds-light; http://pathology.jhu.edu/pc/BasicCauses.php?area=ba; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2020752/;
ANSWERS: 1) death; 2) gene; 3) stomach; 4) cells; 5) weight; 6) smoking; 7) developed; 8) cancer; 9) mutations; 10) cigarette