The Omics Blog by Dr. James Weiss – Part III: Cancer
Great strides have been made in the treatment of cancer. Due to the science of genomics, doctors can offer their patients greater hope both for cure of their disease and also for prevention.
While the term cancer implies only one disease, it actually refers to a very complex set of many diseases. Just because two people may have lung cancer, for example, does not mean they have the same disease nor will they necessarily respond similarly to a given treatment. Genomics is now being used to redefine cancer and provide treatments with a promise of better outcomes. This is a very broad and complex topic and this discussion is meant only as an introduction, not a comprehensive exploration. Let’s look at three points in the care of a patient: before diagnosis and treatment; during care; and in the latter stages of the disease.
In May 2013 Angelina Jolie made front-page news when she revealed that she had undergone a “preventative” double mastectomy. She recently announced that she plans to soon have both of her ovaries surgically removed. Why would an otherwise healthy woman subject herself to such drastic “preventative” surgeries? Because of a strong family history of cancer Ms. Jolie had her two BRCA genes tested. The BRCA1 & BRCA2 genes produce tumor suppressive enzymes that repair damaged DNA and, therefore, help ensure the stability of a cell’s genetic material. She was found to have a faulty BRCA1 gene and thus her cell’s ability to repair damaged DNA was lacking. This imparted a 55 – 65% chance of developing breast cancer vs. 12% in the general population and a 39% chance of developing ovarian cancer vs. 1.4%. She chose the surgery because she could have her increased risk of a potentially life threatening disease literally cut out.
Through sequencing a cancer’s genome it has been shown that a single cancer may actually contain different lines of cells, called clones. Each clone line may actually have its own unique genetics that may cause it to respond quite differently to chemotherapy drugs. One clone might be readily killed by one drug but be resistant to another. This may explain why with the first round of chemotherapy the patient has a good clinical response only to have the cancer come back at a later time. The first round of treatment may kill one line of clones, allowing another to grow in its place. This process may continue until either the cancer is cured or the patient dies. Perhaps a better way of treating an individual would be to identify all of the tumor’s clones prior to treatment and devise, if possible, a cocktail of drugs that will kill all of the cell lines the first time. To do this, the cancer’s DNA must be sequenced prior to the onset of treatment.
Late Stage Treatment:
The words no one with cancer ever wants to hear are, “we are out of options.” This means that the cancer has survived all known available treatments. Whole genome sequencing, of both the patient’s normal cells, as well as the cancer cells, has provided some patients with a treatment for their cancer that would never have been considered without the science of genomics. This 2012 New York Times article (link) is the story of one patient who had a severe form of leukemia. By sequencing his cancer’s genome his doctors found that the leukemia cells were metabolically susceptible to a drug that had only previously been used to treat kidney cancer. This unique approach to treating his cancer saved this man’s life and showed that we may need to start changing our thinking when we consider the most effective way to treat cancer.
The paradigm of how we think about and treat cancer is changing. We are starting to categorize cancers based on genetic similarities, rather than by tissue of origin. The science of genomics may allow doctors to design a treatment protocol that is patient specific with a higher likelihood of cure. In the treatment of cancer we are entering an era of truly personalized medicine.
Read Part I here.
Read Part II here.