Two drugs can help extend the lives of people with colon cancer, the third most common type of tumor in the United States, medical researchers said on Wednesday.

The drugs, tested in two separate studies published in the New England Journal of Medicine, do not cure the disease, which strikes 147,000 Americans each year and kills 57,000.

In one study, scientists found that adding the Genentech drug Avastin to standard chemotherapy for people with advanced colon cancer increased the number of cases where the tumors shrank by more than half.

Just under 45 percent of the 402 volunteers who were given the new drug saw dramatic shrinkage, compared to 34 percent of the 411 patients who received a placebo and standard treatment, according to the study, led by Dr. Herbert Hurwitz at Duke University and financed by Genentech.

The researchers also noted that the drug stretched the average survival time from 15.6 months among the placebo recipients to 20.3 months for those who got Avastin, known generically as bevacizumab.

Avastin is a monoclonal antibody - a lab-made version of a human immune system protein that is set to home in on a target. In this case, it chokes off the formation of blood vessels growing into tumors, giving patients a few more months of life.

“Such a prolongation of survival comes at a price,” said Robert Mayer of the Boston’s Dana-Farber Cancer Institute in an editorial in Thursday’s New England Journal of Medicine.

He said the new treatment, lasting roughly 10 months, will probably run patients $42,800 to $55,000. The drug could be prescribed to up to 40,000 U.S. patients each year at a cost of over $1.5 billion annually, he added.

The results, first presented at last year’s meeting of the American Society of Clinical Oncology, helped convince the U.S. Food and Drug Administration to approve the drug in February.

The medicine is also being tested against breast, lung and kidney cancers.

The second study in the Journal reports on a test of the Sanofi-Synthelabo drug oxaliplatin, also known by the brand name Eloxatin.

That research team found that 78 percent of the 1,123 people who took it in addition to surgery and standard chemotherapy lived cancer-free for three years, compared to 73 percent of a same-size group who got placebos.

The drug seemed to work better on more advanced colon tumors. However, Eloxatin did not increase overall survival.

Although the research team, led by Thierry Andre of Tenon Hospital in Paris, concluded that oxaliplatin improves the treatment of colon cancer, Mayer said the conclusion “is somewhat premature.”