By James C. Salwitz, MD
What does personal medicine mean to you? A doctor who greets with your name and a smile? Caregivers who listen? Physicians who know all about your case and every treatment you have received? We all want doctors who truly understand us. In the near future, this personal understanding will go deeper than ever before.
The instructions for life lie in our chromosomes. Everything about the way our bodies are built is coded in our DNA. Every cell, muscle, nerve, and organ is constructed from genetic blueprints. Tall or short, brown eyes or blue, man or woman, it is all in our genes. Genes define much of who we are and what makes us different. We now understand that genes have a lot to say about the diseases from which we suffer.
Some genes make us resistant to illness. We all know families where everyone lives into their 90s. Other genes increase the risk of specific disease. How often have we met siblings with the same illness? DNA codes how our bodies fight disease or heal from injury. Hard wired in our chromosomes are instructions to make drugs work, fail, or produce side effects. The human genetic code is often the key to health and to disease.
Cancer is a result of damage to our genes. Cancer occurs when the switches inside your genes that control cell growth malfunction. If a growth gene is supposed to be turned off, it turns on. If a genetic switch is designed to prevent cancer growth, it fails. Cells that should be at rest begin to divide, and a tumor develops.
These damaged growth genes are called oncogenes. The damage can occur for three reasons. First, we may be born with a defective gene, such as the BRCA breast cancer gene. Second, exposure to toxins in our environment, such as smoking, can damage our genes. Finally, the genes simply wear out, which partially accounts for the increase in cancer as we age.
Knowing that oncogenes are the key, there can be no doubt that genetic based prevention and therapy will be crucial to winning the war on cancer.
The future: medicine based on our genes
Personalized medicine will be medical care based on our very core. Medicine based on our genes. This will completely change how treatments are given. Today, your physician picks therapies based on research done on thousands of other people. Doctors have only a limited ability to adjust therapy based on individual differences.
Researchers are working toward a future where each of us will have the opportunity to get a blood test to have a complete analysis of the 20,000 coding-genes which is our personal genetic blueprint. This data will be stored in our personal electronic medical chart. It will tell your physician critical information. What diseases are you likely to get? Heart disease? Colon cancer? Arthritis? Alzheimer's? What should be done to help prevent those diseases? Exercise? Yearly colonoscopy? Drugs? Gene therapy? What treatments will work for you, as an individual, and which will harm you?
In the future, if you do get cancer, the tumor itself will be tested. What oncogenes are turned on? What genes are turned off? What caused this to happen? Most important, what needs to be done to turn off those cancer genes and destroy the disease?
Science fiction? Not at all. We are starting to see the first use of personalized medicine techniques now with cancer treatment. Eventually, we will see this type of therapy for all human illness.
Breakthroughs are occurring
Many of the first breakthroughs in personalized medicine have occurred in breast cancer research. The identification of genes linked to breast cancer (BRCA1, BRCA2, CDH1, CHEK2, PTEN, p53, ATM) allows us to warn women and men at increased risk for cancer decades before it might develop. Individuals can then make decisions to help prevent or detect cancer early.
For women diagnosed with breast cancer, genetic testing on the cancer itself can help determine the need for chemotherapy and whether it will work (Oncotype-Dx). Finally, we are using drugs that directly attack targets in breast cancer cells detected by genetic testing (HER2).
Chronic myelogenous leukemia (CML) is a blood cancer. This leukemia is caused by a specific genetic injury called BCR-ABL, also known as the Philadelphia Chromosome. Multiple medications have been created which specifically attack this gene (imatinib, dasatinib, nilotinib). Remarkably, these treatments can be taken by mouth, have few side effects, and in some patients, may actually cure them.
Lung cancer is a menace. Scientists have identified dozens of oncogenes that stimulate its growth. For example, we know that if certain genes are mutated, this leads to rapid lung cancer growth. With information about which oncogene is causing the cancer to grow, specific therapies can be developed to block that gene. The drug erlotinib only works if one type of gene is damaged. The medication crizotinib kills lung cancer by blocking another mutated gene. These treatments, which target specific genes, are resulting in some of the best response rates ever seen in lung cancer. Researchers believe future cancer therapy will consist of drug mixtures to block all activated oncogenes.
Cetuximab and panitumumab are two antibodies that were developed to treat colon cancer. However, at first it seemed as if they were a failure because they did not work in many patients. Then, it was discovered that if a cancer cell has a specific genetic mutation, known as K-ras, these drugs do not work. This is an excellent example of using individual tumor genetics to predict whether or not treatment will work. In the past, the oncologist would have had to try each therapy on every patient and then change when the cancer continued to grow.
A remarkable drug recently came on the market for a disease in which there is often little hope. Metastatic melanoma patients using vemurafenib are outliving patients who do not take the drug. This drug came out of research showing that a key genetic injury in melanoma is the BRAF mutation. Scientists then designed a medicine to attack that mutation.
Last year, more than 40,000 articles were published on cancer care. The most exciting of these related to personalized medicine. Genetic discoveries in brain tumors, pancreatic tumors, liver cancer, kidney cancer, leukemias, myelodyplasia, sarcomas, and oral cancers fill the medical journals. New techniques are being developed to study parts or even the entire genome.
Healthy living makes a difference
Our increased understanding of the genetic basis of disease has helped us realize how important it is that we take good care of our bodies. Smoking, obesity, and alcohol kill by causing DNA damage or exploiting genetic weakness. Exercise and a healthy diet are vital. Genomics will determine how these lifestyle decisions help cause or prevent disease. Personalized medicine will help each of us design lives to decrease the risk of illness and fight it when it occurs.
When Watson and Crick discovered 60 years ago that our bodies were coded in genes, it was an accomplishment with deep and lasting impact. Science has now connected genes and disease. Physicians will use that knowledge to fight illness. Soon, the most personalized statement of medicine will be, "you are cured."
Dr. Salwitz is a practicing medical oncologist in New Jersey and a past president of the Middlesex County chapter of the American Cancer Society.