Doubts over gene testing for cancer therapy
By Marilynn Marchione |
March 21, 2012, Wednesday
|
Print Edition
Print Edition
SCIENTISTS are reporting what could be very bad news for efforts to customize cancer treatment based on each person's genes.
They have discovered big differences from place to place in the same tumor as to which genes are active or mutated. They also found differences in the genetics of the main tumor and places where the cancer has spread.
This means that the single biopsies that doctors rely on to choose drugs are probably not giving a true view of the cancer's biology. It also means that treating cancer won't be as simple as many had hoped.
By analyzing tumors in unprecedented detail, "we're finding that the deeper you go, the more you find," says one study leader Dr Charles Swanton of the Cancer Research UK London Research Institute in England. "It's like going from a black-and-white television with four pixels to a color television with thousands of pixels."
Yet the result is a fuzzier picture of how to treat the disease. The study is reported in New England Journal of Medicine earlier this month.
It is a reality check for "overoptimism" in the field devoted to conquering cancer with new gene-targeting drugs, Dr Dan Longo, a deputy editor at the journal, writes in an editorial.
The study shows that the single biopsy - "the cornerstone of personalized-medicine decisions" - is not enough, Longo writes. And "the simple view of directing therapy on the basis of genetic tumor markers is probably too simple."
About 15 of these medicines are on the market now and hundreds more are in testing, but they have had only limited success. And the new study may help explain why.
1 biopsy not enough
The scientists used gene sequencing to a degree that has not been done before to study primary tumors and places where they spread in four patients with advanced kidney cancer. They found that two-thirds of gene mutations they detected were not present in all areas of the same tumor. They also were stunned to see different mutations in the same gene from one part of a tumor to another.
That means a single biopsy would reveal only a minority of mutations. Still, it's not clear whether doing more biopsies would improve accuracy, or how many or how often they should be done.
Although the study involved kidney cancer, independent experts say the results should apply to other cancers such as breast, lung and colon. And previous research suggests this is so.
"This is an important paper," says Dr Gordon Mills, co-director of the Institute for Personalized Cancer Therapy at the University of Texas MD Anderson Cancer Center.
Doctors say sequencing takes precious time and personalized analysis is still years away from being available in the clinic. It costs US$5,000 to US$10,000 to do basic gene analysis of a major tumor.
They have discovered big differences from place to place in the same tumor as to which genes are active or mutated. They also found differences in the genetics of the main tumor and places where the cancer has spread.
This means that the single biopsies that doctors rely on to choose drugs are probably not giving a true view of the cancer's biology. It also means that treating cancer won't be as simple as many had hoped.
By analyzing tumors in unprecedented detail, "we're finding that the deeper you go, the more you find," says one study leader Dr Charles Swanton of the Cancer Research UK London Research Institute in England. "It's like going from a black-and-white television with four pixels to a color television with thousands of pixels."
Yet the result is a fuzzier picture of how to treat the disease. The study is reported in New England Journal of Medicine earlier this month.
It is a reality check for "overoptimism" in the field devoted to conquering cancer with new gene-targeting drugs, Dr Dan Longo, a deputy editor at the journal, writes in an editorial.
The study shows that the single biopsy - "the cornerstone of personalized-medicine decisions" - is not enough, Longo writes. And "the simple view of directing therapy on the basis of genetic tumor markers is probably too simple."
About 15 of these medicines are on the market now and hundreds more are in testing, but they have had only limited success. And the new study may help explain why.
1 biopsy not enough
The scientists used gene sequencing to a degree that has not been done before to study primary tumors and places where they spread in four patients with advanced kidney cancer. They found that two-thirds of gene mutations they detected were not present in all areas of the same tumor. They also were stunned to see different mutations in the same gene from one part of a tumor to another.
That means a single biopsy would reveal only a minority of mutations. Still, it's not clear whether doing more biopsies would improve accuracy, or how many or how often they should be done.
Although the study involved kidney cancer, independent experts say the results should apply to other cancers such as breast, lung and colon. And previous research suggests this is so.
"This is an important paper," says Dr Gordon Mills, co-director of the Institute for Personalized Cancer Therapy at the University of Texas MD Anderson Cancer Center.
Doctors say sequencing takes precious time and personalized analysis is still years away from being available in the clinic. It costs US$5,000 to US$10,000 to do basic gene analysis of a major tumor.
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