CHICAGO — Many colon cancer patients can cut their chemotherapy regimen in half, improving their quality of life and reducing their chances of having debilitating side effects, according to a major international study released Sunday.

The goal of the research, eagerly awaited by oncologists, was to determine whether a three-month course of chemo was as effective as six months of treatment in staving off a recurrence in people with Stage 3 colon cancer.

The study found that the shorter treatment was almost as effective as the longer treatment; the results were so close that the three-month regimen is likely to become the new standard of care, especially for patients with lower-risk malignancies, researchers said. In addition, the shorter schedule resulted in fewer side effects, such as nerve damage.

“It's really good news,” said senior author Axel Grothey, an oncologist at the Mayo Clinic Cancer Center in Rochester, Minn. “Our goal is to help patients have lower toxicity, while not reducing its efficacy.”

The data is to be presented Sunday as an abstract at the plenary session of the American Society of Clinical Oncology's annual meeting in Chicago. That session features the four studies that are considered to have the greatest potential to affect patient care. The colon cancer research is part of a wider effort among oncologists to carefully ratchet back chemo treatments to lessen side effects and, in some cases, lower costs.

The researchers pooled data from six clinical trials with almost 13,000 colon cancer patients in North America, Europe and Asia. Overall, 74.6 percent of patients who got the three-month therapy were cancer free at three years, compared with 75.5 percent on the six-month schedule.

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And the results were virtually identical for patients with lower-risk disease, defined as cancer that had spread to one to three lymph nodes but not completely through the bowel wall. In that subset, 83.1 percent of patients on the three-month course and 83.3 percent on the six-month schedule were free of cancer three years after treatment.

About 400,000 new cases of Stage 3 colon cancer are diagnosed every year worldwide, Grothey said, with about 60 percent involving lower-risk tumors. Patients with higher-risk disease should discuss the new findings with their doctors to determine whether less chemo is right for them, he said.

For many years, patients with Stage 3 colon cancer have received oxaliplatin-based chemo after surgery to reduce the risk of recurrence. But that medication can cause tingling, numbness and pain in the hands and feet. 

Unlike other side effects, such as hair loss and diarrhea, the nerve damage doesn't end when the chemo ends, Grothey said. Over time, it can become permanent.

Nancy Baxter, head of general surgery at St. Michael's Hospital in Toronto, said the new data would allow doctors to provide a “more personalized approach” to patients with colon cancer. Baxter, who wasn't involved in the study, said it's rare to see research efforts directed at cutting back on treatment, given that such work is of little interest to the pharmaceutical industry.

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