Dr. Bristow’s research, which has been submitted to a medical journal but not yet published, was based on the medical records of 13,321 women with ovarian cancer diagnosed from 1999 to 2006 in California. They had the most common type, called epithelial. Only 37 percent received treatment that adhered to guidelines set by the National Comprehensive Cancer Network, an alliance of 21 major cancer centers with expert panels that analyze research and recommend treatments. The guidelines for ovarian cancer specify surgical procedures and chemotherapy, depending on the stage of the disease.

Surgeons who operated on 10 or more women a year for ovarian cancer, and hospitals that treated 20 or more a year, were more likely to stick to the guidelines, the study found. And their patients lived longer. Among women with advanced disease — the stage at which ovarian cancer is usually first found — 35 percent survived at least five years if their care met the guidelines, compared with 25 percent of those whose care fell short.

But most of the women in the study, more than 80 percent, were treated by what the researchers called “low-volume” providers — surgeons with 10 or fewer cases a year, and hospitals with 20 or fewer.

Dr. Bristow said women should ask surgeons how often they operate on women with ovarian cancer and how often they achieve complete debulking. But he also acknowledged that many patients hesitate to ask for fear of offending the doctor who may operate on them.

Ovarian cancer has unusual traits that make it more treatable than some other cancers. It is less likely to spread through the bloodstream and lymph system to distant organs like the lungs and brain. The tumors do spread, but usually within the abdomen and pelvis, where they tend to coat other organs but not eat into them and destroy them, said Dr. Matthew A. Powell, a gynecologic oncologist and associate professor at Washington University School of Medicine in St. Louis.

And most ovarian cancers are extremely sensitive to chemotherapy, experts said.

In 2006, a study was published that many doctors thought would change the field forever. It compared standard intravenous chemotherapy with a regimen that pumped the drugs directly into the abdomen. The test regimen was highly toxic, and not all patients could tolerate it. But median survival on it was 65.6 months, compared with 49.7 months on the standard treatment — a survival difference of 15.9 months.

The gain was huge, almost unheard of. New cancer drugs are often approved if they buy patients just a few months. The test treatment — called intraperitoneal, or IP therapy — did not even use new drugs. It just gave the old ones in a different way. Several previous studies had had similar findings for IP therapy, but the 2006 study, led by Dr. Armstrong, had the most definitive results.