Cancer is the second largest cause of death in industrialized countries. Frequency of cancer increased significantly in the last decades, and most experts consider this as a reflection of the fact that now we live longer and rarely die from infectious diseases. Cancer is more common in older patients who reached post-reproductive age.
Inherited genetic mutations increase chances of developing cancer
Usually cancer is connected to environmental factors such as pollution, bad habits (smoking, alcohol), poor diet, obesity and lack of physical activity. However, many people have increased chances of cancer due to genetic predisposition. The highest percentage of such cases is observed among patients with breast cancer, prostate cancer and ovarian cancer.
The presence of hereditary componentwas established long ago for many familial cancers but the exact genetic reasons behind the pattern were discovered only relatively recently.
Some genes confer much higher chances of cancer while others only increase the probability of cancer development by only few percents. For instance, mutations in genes BRCA1 and BRCA2 are often associated with a very high risk of breast cancer. The carriers of these defective genes, in combination with other genetic factors, may have up to 50% chances of getting breast cancer during their lifetime, compared to one in eight chances for average women.
Obviously, those who have higher than average chances of getting cancer need to take extra care of their health and should be monitored. Reliable identification of those at higher risk, however, is not an easy task. In some cases, family history of cancer can provide certain clues, but on its own the family history analysis is not very reliable. Detection of some more common cancer-associated genes like mutated versions of BRCA1 and BRCA2 can be done easily. The problem, however, is that very often cancer predisposition is multi-factorial, and in each individual case many different genes can be involved. Detailed genetic analysis is the best way of identifying the vulnerable individual and taking care of them.
The number of cancer related genetic markers is growing fast
The studies performed by scientists from several British universities have identified more than 80 new cancer genetic markers. Researchers analyzed the DNA of 200,000 people looking for small changes associated with cancer. The findings were published earlier this year in several research papers. After publication of these results, the number of genetic alterations associated with breast cancer increased to 76. Now we are also aware of 78 genetic risk factors leading to prostate cancer and 12 genes associated with ovarian cancer. We also know a number of genes that reduce the probability of cancer.
How To Identify People At High Risk Of Getting Cancer?
With such a large number of genes that can increase the chances of developing various malignancies, correct identification of individuals at risk is not an easy task. Separate testing for the presence of each and every potential genetic marker of cancer is difficult, impractical, time-consuming and expensive. Novel approach involves the use of panels of genetic markers and performing the whole analysis in one experiment. These multi-gene platforms give the full picture of genetic situation in each particular case. Having full information allow the precise calculation of risk and facilitate the decision-making regarding the monitoring or preventive treatment of patients.
Multi-gene panel of tests screening for 46 cancer related genes is now in use in Oxford hospitals in the UK. The system was introduced this year as a pilot project and will be extended to other part of British National Health Service later this year. Individual test costs 300 British pounds (approximately US$ 450) but the test can save much more by putting the patients on the right treatment straightaway. New test panel that will analyze 150 genes is currently under development.
The best technique that can help in predicting the cancer risk is the full sequencing of patient’s genome. Not so long ago this task looked practically impossible and prohibitively expensive. But in the last few years, with the fast progress in genome sequencing, full sequencing increasingly looks like the viable and economically sound approach. The cost of full individual genome sequencing, with analysis and interpretation, is now estimated at approximately US$ 5,000. Some vendors offer it as cheap as $1,000. This is comparable with the cost of colonoscopy.
Full knowledge of genome for each patient can help in predicting the risk of other, not cancer related diseases and conditions and help in choosing the best therapeutics for each patient.
What can be done for those with identified risk of cancer?
The knowledge of detailed individual information can help to predict the risk of cancer fairly accurately. What can be done to prevent cancer in individuals at higher risk? Better and regular targeted monitoring is one of the options. Early diagnostic techniques are improving fast these days and can help to find cancer at very early stages when it is curable. Early detection helps to choose the best treatment methods. When cancer is detected early, surgical removal can be done easily and the use of health damaging techniques such as radiation and chemotherapy can be avoided.
In some cases such as breast cancers with very high genetic predisposition, preventive measures can be taken. Some women with these unfortunate genetic anomalies opt for prophylactic bilateral mastectomy (surgical removal of both breasts) which reduces the risk of disease by 90%. Pharmaceutical prevention can be also used. For instance, tamoxifen, a relatively safe drug against breast cancer can be taken by high risk patients as a preventive measure. Taking tamoxifen for several years decreases the risk of breast cancer almost twice.