Mon 24 Sep 2018
The use of DNA sequencing to look for specific mutations is only applicable to a relatively small proportion of cancer patients
Medscape Pathology, an online information source for doctors has just published an interesting article by Liz Szabo, a senior correspondent for Kaiser Health News. The article is entitled “'Precision Medicine' Often Misses the Target”. It tells the story of MaryAnne DiCanto a 55 year-old woman facing incurable breast cancer. MaryAnne DiCanto put her faith in “precision medicine” and she and her husband spent a large amount of money over a 13-year period pursuing the specific drug which might work for her tumour. Over the years she underwent repeated biopsies to obtain tissue for DNA sequencing to look for specific mutations that might reveal susceptibility of her tumour to one of the new precision medicine drugs.
Liz Szabo points out how doctors and hospitals love to talk about the patients they’ve saved with precision medicine, and reporters love to write about them. But the people who die — patients like DiCanto, who succumb to advanced cancer despite the advanced testing — still vastly outnumber the rare successes.
Testing for genetic mutations has become the standard of care in lung cancer, melanoma and a handful of other tumor types. But the number of people with advanced cancer eligible for these approaches is just 9 percent to 15 percent, experts estimate. These targeted therapies help only about half of patients who are found to be eligible to try them, said Dr. Vinay Prasad, an associate professor at Oregon Health and Science University. Targeted therapies tend to be less successful in patients like DiCanto, who have exhausted all standard treatments. In a large study published last year in Cancer Discovery, precision medicine failed to help 93 percent of the 1,000 patients who signed up for the study. At the most recent meeting of the American Society of Clinical Oncology — the largest cancer meeting in the world — researchers presented four precision-medicine studies. Two were total failures. The other two weren't much better, failing to shrink tumors 92 percent and 95 percent of the time.
Scott Primiano, Maryanne’s husband said patients should remember that precision medicine is in its infancy. Although scientists have identified tens of thousands of genetic "variations" — changes from normal DNA that could play a role in cancer — doctors have only a few dozen drugs with which to target them. In the majority of cases, genetic mutations are of "unknown significance"; they’re essentially useless, because scientists don’t know if they affect how patients respond to drugs.
Even when drugs are a good match for a specific mutation, they don't always work. A targeted therapy that works in melanoma, for example, doesn't help people with colorectal cancer — even when patients have the exact same mutation, said Wagle, a member of the medical advisory board for Living Beyond Breast Cancer, a patient advocacy group in which DiCanto was active.
Primiano worries about people with fewer resources than he and his wife, especially patients tempted to drain their savings account to pay for a treatment with little to no chance of working. The very words "precision medicine" suggest a high rate of success, Primiano said. While its successes should be celebrated, its failures must be acknowledged and tallied, reminding us how much is left to learn. When patients and their families have so much on the line, they deserve to understand what they’re paying for. "Let’s not pretend this is something it isn’t,” Primiano said. “I’m not saying we shouldn’t try it. I just don’t want people to have false hope."
Full article on Medscape Pathology (you will need to create a login to access the full article).