Twenty-two years ago, California legislators gave researchers a long-coveted tool, requiring state health officials to gather detailed information on the incidence and treatment of cancer. Today, the California Cancer Registry is a vast gold mine, containing demographic data and other nuggets of information on more than 2.5 million cancer cases.

UC Davis researchers have been quick to pounce on the voluminous files. Now, in a unique collaboration with registry staff, the university’s oncologists are targeting cancers that strike women.

Powered by the registry’s richly detailed data, researchers are documenting cancer trends, illuminating disparities in treatment and unearthing a string of findings that are helping to guide patient care.

They have produced sometimes provocative reports on ovarian, cervical and endometrial cancers, and published a series of papers investigating the outcomes of cancers in pregnant women. In one high-profile study, appearing in a 2005 issue of the journal Cancer, UC Davis researchers dispelled the long-held view that pregnant women with melanomas fared worse than those who were not carrying a child.

"There was a belief that the pregnancy milieu made the melanoma progress faster, and, in some instances, pregnant women diagnosed with the cancer were even advised to abort the fetus," says Rosemary D. Cress, research program director for the registry. "So the study showing there was actually not a difference in how pregnant women fared was really significant."

The collaboration on women's cancers was launched in 1999, when former California Sen. Debra Ortiz (D-Sacramento) and other lawmakers set aside about $300,000 for the work.

"While quite a lot of money has been dedicated to studying breast cancer, some of the other women's cancers had not been as heavily investigated," says Cress, who sparked the partnership with UC Davis oncologists. "The grant was intended to help us close that gap. And, fortunately, I found researchers at the cancer center who were as excited about the prospects as I was."

One of the earliest enthusiasts was Gary S. Leiserowitz, professor and chief of the UC Davis Division of Gynecologic Oncology. Leiserowitz calls the work rising from the registry's population data a vital report card on patient treatment.

"The cancer registry is a great and powerful guidebook," he says. "It can illustrate disparities in treatment and patterns of care that might not meet our expectations. And then we can do something about that."

Housed in a nondescript office building in Sacramento, the registry first began collecting data in 1988, three years after the Legislature required health officials to establish a statewide cancer reporting system. Each year, more than 140,000 new cases of cancer are added to the registry's files.

The database includes information on patient demographics, cancer type, extent of disease at diagnosis, treatment and survival. In authorizing its creation, lawmakers hoped the availability of information on cancer statewide would help researchers tease out geographic, ethnic, occupational and other differences, providing clues about risk factors. The data also helps shape policy, revealing where early detection, educational or other cancer-related programs should be directed.

In addition, the registry publishes reports each year summarizing statewide cancer case rates and deaths, changes in rates over time and differences according to age, race/ethnicity and types of cancer. Because of California's multi-ethnic population, more is now known about the occurrence of cancer in diverse communities than ever before, making the registry a cornerstone of a substantial amount of research.

The registry's size makes it particularly valuable. Covering more than one-tenth of the United States population, the registry allows researchers to identify associations that might not be apparent in smaller samples, such as an individual cancer center.

"It's a very broad sweep," Leiserowitz says. "The law requires hospitals and radiation oncology centers to report on their cases, and compliance is very high, approaching 100 percent. So we really are capturing most of the data about patients in California, and there is rich detail about the kinds of cancers and their outcomes."

For Leiserowitz, the registry provides a "reality check" for oncologists and policymakers by documenting disparities in cancer treatment in the community. Those disparities, he says, may relate to income or education level, ethnicity or other cultural factors. Findings can then be used to guide political decisions about where to allocate health-care dollars.

Because the registry's data is relatively unfiltered, researchers must be careful not to overreach, Leiserowitz says. In some instances, he notes, two experts could look at the same records and draw very different conclusions about what it all means.

"It's easy with these population-based studies to see things that may not be there," Leiserowitz acknowledges. "And sometimes the explanations for what we see aren't as nefarious as we initially believe."

One ongoing series of reports anchored in registry data centers on the outcomes of cancers in pregnant women. The work was spearheaded by Lloyd Smith, professor and chair of the Department of Obstetrics and Gynecology at UC Davis.

Smith had the novel idea of linking registry cases with a database of hospital deliveries. That approach has led to a variety of reports – including the study on melanoma during pregnancy – that have illuminated the incidence and risks of these cancers. Leiserowitz, for example, used the data to show that although ovarian masses are relatively common during pregnancy, they are not typically malignant, allowing many women to avoid surgery while pregnant.

In perhaps the most widely noticed of these studies, Smith and Cyllene Morris, a registry research scientist, helped dispel the long-held myth that ovarian cancer is a "silent disease," announcing itself only at the late stages when prognosis is poor. Instead, the study found that patients with ovarian cancer were more likely than two groups of other patients to report symptoms such as abdominal swelling and pain. The symptoms were reported at least four months – and, in some instances, as long as a year – before the patients with ovarian cancer were diagnosed.

"Dr. Smith showed that these women do in fact have symptoms that are often misinterpreted by their physicians, often leading to a delay in diagnosis," Leiserowitz says. "Ovarian cancer, he found, is really not a silent disease at all."

For Cress, such findings are a gratifying payoff from the partnership between the registry and the cancer center. Moreover, she notes, they are merely the start of what researchers may find as they comb through the registry's ever-expanding files.

"The collaboration has been terrific, and there is so much more that could be done," Cress says. "The projects are limited only by the imagination of the scientists."