When Elana Simon was 12 years old, she was diagnosed with a rare form of cancer that required an operation to remove much of her liver.

Now 18, Ms. Simon, a high school senior, dancer and aerial acrobat, is deemed cancer-free. She also is a key member of a research team that has identified a genetic abnormality that may be a cause of the mysterious cancer, which afflicts about 200 adolescents and young adults a year world-wide.

Ms. Simon initiated the study and worked closely with scientists at Rockefeller University, where her father runs a laboratory, as well as at Memorial Sloan-Kettering Cancer Center and New York Genome Center, all in New York, to conduct genetic sequencing and other analyses. The findings were published Thursday in the journal Science.

The disease, called fibrolamellar hepatocellular carcinoma, has no effective drug treatments, and without surgery, prognosis for patients is poor.

The genetic anomaly Ms. Simon and her colleagues found is a fusion of parts of two different genes. It turned up in tumor tissue taken from all 15 patients they studied, while it wasn't present in any normal liver tissue removed from the same patients—a strong signal that the mutant gene could be a culprit, researchers said.