I wish the answer to that question was a simple “yes.” In that perfect world, we could perform an easy blood test or swab that provided a definitive answer about a person’s short term and long term likelihood of getting cancer and use that information to formulate a strategy to decrease her risk. Unfortunately, as you have probably guessed, it is nowhere near that simple. The “C” word is a looming fear in the minds of many people and particularly those whose lives have been touched by a friend or family member affected by cancer. The desire to have a way to know ahead of time and to intervene in some way to prevent the development of cancer down the road is certainly understandable.
Mapping the human genome has expanded our knowledge on the genetic basis of a variety of diseases. Think of the genome as a library contained in each one of your cells. This library is full of books where each book represents a gene and several genes are grouped together on a book shelf which represents a chromosome. The letters that make up the words in each of those books is the genetic code. The human genome project in this metaphor is actually making a card catalog of the bookshelves and identifying what books/genes are on which bookshelves/chromosomes. Multiple studies have been performed in which researchers have looked at the whole genome of participants in the study who either have or do not have a certain type of disease/condition, and they have noted variations in the coding material (content on the books) at specific locations on certain genes that are more common in people who have the disease compared with those who don’t have it. These are called genome wide association studies. We are now getting to a time when research labs and companies are attempting to find clinical applications for this information, in other words, find ways to make this information useful to patients by developing testing. Some of these observed variations in the genetic material are associated with a greatly increased risk for cancer, others with an intermediate increased risk of cancer, and others associated with a low increased risk of cancer. One of the more well-publicized tests is for a mutation in the BRCA 1 or 2 genes, which is passed down through families and has a strong association with development of early breast and ovarian cancer.
In order for a test to be useful, we have to know that we can trust the information, that we have a clear idea of what to do with a positive/negative test result, and that there is something we can do that changes an outcome down the line. Additional issues that arise with these genetic tests pertain to the implications of positive tests on the person being tested and her family, privacy and non-discrimination for carriers of a gene, positive results on a low or intermediate risk gene, and what to do is testing is inconclusive. Some of the genetic testing identifying gene variations that are weakly associated with increased risk of cancer do not have sufficient studies to provide the physician a good guidelines as to what to do with the positive results. The presence of these gene variations may minimally increase a person’s risk in reality but could cause significant distress to the person receiving the results.
The American Society of Clinical Oncologists has provided guidelines to physicians about offering genetic tests for cancer susceptibility as more and more of these tests are developed and potentially put on the market. Three criteria should be met for testing: the individual being tested has a personal or family history suggestive of genetic cancer susceptibility, the genetic test can be adequately interpreted, and the test results have a proven clinical utility. Testing for BRCA mutations in individuals with a family history of clustered breast and ovarian cancer or testing for Non-polyposis Hereditary Colorectal Carcinoma (NPHCC/Lynch Syndrome) in individuals with a strong family history of colon cancer and endometrial cancer are two examples of testing that meet the ASCO criteria.
The gray area comes into play with testing using single nucleotide polymorphisms (SNPs) which are essentially changing one word in the book that represents a gene in a person’s genetic library. Some of these variations are meaningful and some may not be. Making sure the conclusions we can feel secure in drawing from the test results of tests using SNPs is important before offering them to our patients. We do not want to generate a false sense of alarm or security. We also do not want to have tests results that we do not know how to appropriately counsel a patient about.
The majority of breast and ovarian cancers are not due to one defective inherited gene. About 10% of breast cancers and 15% of ovarian cancers are the hereditary type. The rest, representing the majority, are due to accumulations of errors we develop over a lifetime.
As women, breast, ovary, uterine, colon, and lung cancer probably rank highest on the list of cancer concerns. Traditional screening for breast cancer includes clinical breast exams and mammography. Ovarian and uterine cancers do not have great screening tests and are typically detected when an ovarian mass is discovered on examination or on sonography or CT scan during a work up for abdominal or pelvic pain or abnormal bleeding. Colon cancer screening typically involves colonoscopy, sigmoidoscopy, or yearly evaluation of multiple stool specimens for blood. Initiation and interval for screening are adjusted based on risk factors including a person’s family history.
For hereditary breast and ovarian cancer, a genetic test for a mutation in the BRCA 1 or 2 gene is available. This test is appropriate for women with certain types of ovarian cancer or a combination of a personal and family history of multiple members with breast and/or ovarian cancer.
For sporadic breast cancer, BrevaGen has a developed a test of several SNPs independently associated with increased risk of breast cancer (some low and some intermediate risk) that can be combined with clinical risk factors to adjust 5 year and lifetime breast cancer risk. It has not been approved for use in all patients yet.
For hereditary colon and endometrial cancer, testing is available for Lynch Syndrome, which may be appropriate in families with multiple members developing colon or endometrial cancer younger than 50.
Lung cancer is the leading cause of cancer death in women in the United States. The overwhelming risk factor in the development of lung cancer is tobacco smoking. Smoking takes a person’s risk of developing lung cancer from < 1% to about 14%. Bottom line, do not ever start smoking. If you already smoke, quit. Although it may be easier said than done, it can be done. There does seem to be some clustering in families of lung cancer beyond what their risk would be from smoking alone, suggesting a genetic component to it as well. This adds to a patient’s risk particularly when he/she smokes. While some variations have been identified on certain chromosomes that researchers suspect might contribute to this genetic component, this information has not been put into a screening test yet.
Information available on:
cdc.gov (Centers for Disease Control)
cancer.org (American Cancer Society)
nsgc.org (National Society for Genetic Counselors)