For their new study, the scientists examined cancer samples from the Cancer Genome Atlas, as well as cancer samples from the Broad’s own collection. All told, they analyzed 4,742 samples from 21 types of cancer.

The new study detected many of the genes that other scientists have previously linked to those 21 types of cancer. But they also found new genes that had been overlooked before. All told, they identified 33 genes that they consider strong candidates for playing a role in cancer — a potential increase of the catalog of cancer genes of 25 percent.

“This was eye-opening to me,” said Dr. Lander.

Dr. Lander and his colleagues began to wonder how many genes could be found if scientists looked at more cancer samples. Was the cancer catalog almost finished, or only just begun?

“We were able to ask for the first time, ‘Are we there yet?'” said Dr. Lander.

They extrapolated from their own results to gauge how many more samples scientists would need to look at to find most cancer genes involved in at least 2 percent of cancers of a given type.

To find most cancer genes involved in the 50 most common types of cancer, the researchers estimated that they would have to analyze 100,000 samples. In other words, the atlas has gotten us a tenth of the way to the finish line.

Dr. Harold Varmus, the director of the National Cancer Institute, said the study has raised valuable questions. “The paper provides some models about what we might think about doing next,” he said. He said the agency is now considering testing Dr. Lander’s hypothesis on a few types of cancer by gathering more samples.

Dr. Lander and his colleagues argue for finishing off the cancer gene catalog. “Completing the genomic analysis of this disease should be a biomedical imperative,” they wrote in their new paper.