Current practice of only focusing on tumor samples might adversely affect care
WebMD News from HealthDay
By Dennis Thompson
HealthDay Reporter
WEDNESDAY, April 15, 2015 (HealthDay News) -- If genetic tests are only done on cancer tissue, as many as half of patients may not receive the most appropriate treatment for their cancer, a new study reports.
Cancer doctors increasingly rely on genetic testing to look for opportunities to use treatments that target specific genetic causes of cancer -- called targeted therapy.
But doctors often examine just the genetics -- or DNA -- of a patient's cancerous tissue, and don't compare it against a genetic analysis of normal tissue, explained study senior author Dr. Victor Velculescu. He is a professor of oncology and pathology at Johns Hopkins University School of Medicine, and co-director of the school's Cancer Biology Program.
The problem is that it's not unusual for people to have genetic variations in normal tissue that aren't causing cancer. By ignoring a person's normal genetics and only looking at the genetics of the cancer, doctors can be fooled by those normal variations and assume that these harmless mutations are the cause of the patient's cancer, the researchers found.
Their findings show that unless doctors compare the DNA of cancerous tissue to normal tissue, they run the risk of misjudging the genetic causes of a person's cancer about half the time.
"These false positive changes affected roughly one in every two patients analyzed," said Velculescu. "In other words, one in two patients receiving tumor-only gene panel sequencing is potentially at risk to receive a treatment that may be inappropriate."
Treatments based on the wrong genetic diagnosis could range from merely ineffective to potentially harmful, and all at a great financial cost, Velculescu said. Targeted cancer therapies are some of the most expensive medications on the market, and can have very severe side effects, he added.
The study was published April 15 in the journal Science Translational Medicine.
For the study, the researchers compared the genetic information of tumor and normal tissue from 815 patients. These patients had a variety of cancers, including breast, brain, renal, gastric, lung, pancreatic, and blood cancers and melanoma.
source : Cancer Gene Tests Should Include Healthy Tissue, Too: Study
