In the last few days before Congress left for its campaign recess, legislation to promote research on the deadliest cancers looked like it was on the fast track to the president’s desk.

The bill had overwhelming bipartisan support. Nearly 300 members co-sponsored it in the House, where it passed Sept. 19 by voice vote under an expedited process. Earlier that day, the Senate Health, Education, Labor and Pensions Committee had approved a companion measure, also by voice vote. That bill already had been negotiated with the House, said Chairman Tom Harkin, D-Iowa.

But even a cancer research bill can draw opposition, this time from Republican Sen. Tom Coburn of Oklahoma. Coburn, a three-time cancer survivor, is not against research to fight the disease. But he is opposed to Congress giving orders to researchers. So, for now at least, he is holding up the bill (HR 733).

Coburn’s concerns about the measure, as well as similar ones expressed by the head of the National Cancer Institute, have not deterred supporters of the bill, and they return to Capitol Hill this week with a renewed sense of purpose.

“We are still determined and committed to getting it done this Congress,” said Julie M. Fleshman, president and CEO of the Pancreatic Cancer Action Network.

She said her organization is asking people to write their senators to urge support and is also staying in touch with the bill’s sponsors to find a way to get the measure passed.

In addition, “the House and Senate leaders of the bill are working together to address Sen. Coburn’s concerns,” said a spokesman for House sponsor Anna G. Eshoo, adding that supporters “remain optimistic it can pass this session.”

The legislation already has undergone changes to address earlier concerns raised by lawmakers, the cancer institute and other parties, according to the Pancreatic Cancer Action Network. As introduced, for example, the bill included authorizations for funding that were removed by a House subcommittee because many members of Congress were resistant to measures linked to potential spending in the current fiscal climate.

Also, the original bill focused on research aimed just at pancreatic cancer, but lawmakers were worried about pushing disease-specific legislation. So sponsors expanded its scope to include “recalcitrant cancers” — defined as those cancers with five-year survival rates of less than 50 percent.

Under the bill’s current language, the National Cancer Institute must identify at least two recalcitrant cancers with five-year survival rates of less than 20 percent that are estimated to cause at least 30,000 American deaths each year. The two cancers that meet that definition are pancreatic and lung cancer, according to the Pancreatic Cancer Action Network. The five-year survival rate for lung cancer is 16 percent, while pancreatic cancer’s is 6 percent.

The institute would then be required to develop a scientific framework to guide research on each of the cancers. At the agency’s discretion, the program could be expanded to other recalcitrant cancers.

But Coburn says the National Institutes of Health, which the cancer institute is part of, should be able to make its own research decisions. In his letter to Senate Minority Leader Mitch McConnell, R-Ky., in which he asked to be consulted before the bill moves forward, the Oklahoma senator said research plans should be established when the NIH finds they are needed or when congressional oversight determines the agency’s work on an issue has been significantly lacking. The latter has not occurred in this instance, he said.

Coburn, who is a physician, said he especially disagrees with congressional requirements that the NIH maintain “an outdated disease-by-disease approach” when current biomedical research looks at broader questions across different disciplines.

“Congressional mandates will not serve to speed up the pace of science, but only hamstring the ability of NIH to respond to emerging breakthroughs,” he wrote.

NCI Director Harold Varmus also expressed concerns about the legislation’s focus, saying there’s a danger the bill would spur more advocacy groups to push Congress for new requirements. Instead, Varmus said, lawmakers should be focused on preventing the automatic spending sequester from taking effect, as well as concentrating on foreign affairs and the economy.

“A message in report language would be perfectly adequate to indicate to us that Congress is interested in hearing something about this topic, and we would comply with the report,” he said.

But Fleshman said her group has secured language on pancreatic cancer in past report language accompanying appropriations bills and wasn’t satisfied with the response.

In 2007, the network began having discussions about legislative options. Eshoo introduced a bill a year later that would have established a Pancreatic Cancer Initiative and required a strategic plan to advance pancreatic cancer research. That measure was reintroduced in the subsequent congresses and modified in September before advancing.

“The reality is, the NCI actually could do these things on their own. But because they weren’t happening on their own, you know, we decided that it was time to introduce legislation,” Fleshman said.

Rebecca Adams contributed to this report.