Drugmakers may be forced to change prescribing info on cancer meds already being sold in the US to advise patients that some treatments won’t work in people who carry certain genes,Bloomberg News writes.
Prescribing drugs on the basis of genetic profiles can limit use of medicines to patients who will benefit most and increase their safe use, FDA staffers wrote in briefing materials for an advisory committee meeting on December 16. The change may also hinder sales of drugs that previously might have been given to more people, just on the chance they may work.
The meeting is being held to discuss whether to recommend that doctors screen patients for the so-called KRAS gene mutation before prescribing Erbitux, which is marketed by Lilly and Bristol-Myers Squibb, and Amgen's Vectibix, which are used to treat colon cancer. The drugs, which cost $8,000 to $10,000 a month, don’t work in people with the mutation.
“We’re going to see this story played out over and over again,” Richard Schilsky, a University of Chicago cancer specialist who is president of the American Society of Clinical Oncology, tells Bloomberg. "This is the kind of change that’s about where cancer drugs should be moving. They shouldn’t be used in those with no chance of benefit.”
Researchers estimate 40 percent of colon cancer patients have the KRAS mutation, which would make them ineligible to get Erbitux or Vectibix. Prescribing according to the mutation may not necessarily reduce Erbitux sales, as more patients would be tested and the pool of individuals that would benefit from the drug may increase, Les Funtleyder, an analyst with Miller Tabak, tells Bloomberg.
Last year, Erbitux generated $1.3 billion in sales and Vectibix rang up $170 million. Almost 150,000 people in the US will be diagnosed with colorectal cancer this year, according to the American Cancer Society data cited by Bloomberg.
Testing for a genetic variant known as HER-2 is already required for Genentech’s Herceptin breast cancer med, which treats tumors that produce too much of the HER-2 protein. The KRAS discovery came after Erbitux and Vectibix were on the market - in the US, Erbitux was approved in 2004, and Vectibix in 2006.
“An ideal scenario is one in which the relationship of the biomarker to potential action of the drug is recognized very early - indeed, such a relationship might be the motivation for starting the drug’s development,” FDA reviewers wrote in briefing documents. “The ideal scenario is a rarity to date.” In studies, Erbitux and Vectibix reduced by 30 percent the risk that colon cancer worsened. Subsequent analyses found patients with a normal KRAS gene did much better than those with mutations. “The consistency across studies makes this data really strong,” Fouad Namouni, executive director of oncology for Bristol-Myers Squibb, tells Bloomberg. Reducing by 40 percent the number of patients who spend on those drugs may benefit “society at large."
“The whole concept of proper genetic markers is not to put people in the position of having to receive toxic medicines if they’re not going to do any good,” Ira Loss of Washington Analysis tells Bloomberg. “The FDA probably feels that’s an improvement over giving it to everybody and hoping for the best.”
The National Comprehensive Cancer Network recommended genetic screening last month because of the studies. Tests for the KRAS mutation involve analyzing a sample of tissue from a patient’s tumor. The effort is also part of an FDA drive to identify which genes interact with drugs. A few meds already require genetic testing before being prescribed, and the FDA created an initiative to discover more.
In July, Bloomberg points out, the FDA recommended testing patients for a gene, called HLA-B-5701 that causes a reaction in patients taking Glaxo’s Ziagen AIDS drug. Last month, the agency reported that people with a gene dubbed HLA-B-5702 have an increased risk of skin reactions from Pfizer’s seizure drugs Dilantin and Cerebyx.