Dr. Richard Schilsky, a professor of medicine at the University of Chicago, said the number of cancers diagnosed in a year was easy to predict. “So we ought to be able to make a pretty good estimate of the grams required to treat every patient in the country in any given year,” he said.

Legislation proposed in both the House and the Senate would give the Food and Drug Administration the power to demand that drug makers give early warnings of possible supply disruptions. Senator Amy Klobuchar, Democrat of Minnesota, said the idea behind the bipartisan bill came after she found that the agency had prevented 38 shortages last year after getting early alerts of problems at drug makers.

“I can’t say the drug companies are excited” about the proposed legislation, she said in an interview. “But we need to give the F.D.A. more time.”

A group of leading oncologists has started a not-for-profit drug company that it hopes will soon be able to import supplies of some of the missing medicines. The company will eventually manufacture the drugs itself, according to Dr. George Tidmarsh, a pediatric oncologist and biotechnology entrepreneur who will lead it.

“We have a meeting with the F.D.A. next week,” Dr. Tidmarsh said. “This unfolding tragedy must stop, and right now.”

More than half the recent shortages have resulted because government or company inspectors found problems like microbial contamination that can be lethal on injection. Others have occurred because of capacity problems at drug plants or lack of interest because of low profits, according to the F.D.A.

Doxil, the cancer drug Ms. Nomikos needs, is made by Johnson & Johnson. Monica Neufang, a company spokeswoman, said, “Our third-party manufacturer has had some manufacturing issues related to capacity.”