A new study has found widespread failure among doctors to follow clinical guidelines for treating ovarian cancer, which kills 15,000 women a year in this country. This disturbing news shows the kind of challenge that health care reformers are up against in improving medical care — even when cost is not the issue.

The study, presented at a conference on gynecologic cancers on Monday, analyzed the treatment of more than 13,000 women with ovarian cancer who received their diagnoses between 1999 and 2006. Only 37 percent received the care recommended in guidelines set by the National Comprehensive Cancer Network, an alliance of 21 major cancer centers.

This kind of failure is not uncommon in American medicine. A decade ago, RAND Corporation researchers reported that just 55 percent of a large sample of patients suffering from a broad range of diseases received care that met quality guidelines. Numerous studies since then focusing on specific diseases have found similar problems.

In the case of ovarian cancer, the consequences of inadequate care are tragic. The recommended guidelines specify combinations of surgery and chemotherapy, depending on the stage of the disease, including debulking surgery to remove all visible traces of the tumor and aggressive chemotherapy that can prolong life. Women who received the recommended treatment were 30 percent less likely to die than those who did not. Among those with advanced cancer, the stage at which ovarian cancer is usually first found, 35 percent of the women treated in accordance with the guidelines survived at least five years compared with 25 percent for those whose care fell short.