Friedman made his recommendation at a meeting of the American Cancer Society that concluded yesterday in San Diego.
President Reagan was operated on for colon cancer almost two years ago, but did not receive chemotherapy.
"This information has taken a long time to evolve," Friedman said. "Were such a patient (as Reagan) present today, I think he should be considered for chemotherapy."
Colo-rectal cancer is the second-biggest killer among cancers, after lung cancer. Friedman said 140,000 new cases would be diagnosed in the United States this year.
In almost one-quarter of the patients, the cancer will be too widespread to remove, he said. But the rest - 106,500 this year - will have surgery. Of these, 62,000 will survive at least five years.
The other 44,500 probably will not be cured because some cancer will be left behind after surgery. Friedman says these patients might benefit from chemotherapy.
"Until recently, there has been considerable controversy whether any adjuvant therapy (in addition to surgery) affected the outcome of patients after surgical treatment," he said. "It is now apparent that there is effective therapy and that many patients simply have not been receiving anything because their physicians saw no reason for giving them anything."
He estimated that an additional 6,000 patients with colon cancer and 5,000 with rectal cancer could be cured "if these therapies were uniformly and appropriately applied."
Deaths from colon and rectal cancer have declined 23 percent since 1950, said Vincent T. DeVita Jr., head of the cancer institute. "I think that's a treatment-related decline," although earlier detection of the disease and better surgical techniques also played a role, he said.
Friedman said that it still was not clear which chemotherapy drug worked best, and that new research would be needed to compare medicines.
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