When Dr. Marc Chamberlain, a Seattle oncologist, was treating his brain cancer patients, he noticed an alarming pattern. His male patients were typically receiving much-needed support from their wives. But a number of his female patients were going it alone, ending up separated or divorced after receiving a brain tumor diagnosis.

Dr. Chamberlain, chief of the neuro-oncology division at the Fred Hutchinson Cancer Research Center, had heard similar stories from his colleagues. To find out if these observations were based in fact, he embarked on a study with Dr. Michael J. Glantz of the University of Utah Huntsman Cancer Institute and colleagues from three other institutions who began to collect data on 515 patients who received diagnoses of brain tumors or multiple sclerosis from 2001 through 2006.

The results were surprising. Women in the study who were told they had a serious illness were seven times as likely to become separated or divorced as men with similar health problems, according to the report published in the journal Cancer.

Over all, about 12 percent of the patients in the study ended up separated or divorced, a rate that was similar to that found in the general American population during that time period. (Lifetime divorce rates in the United States are higher.) But the pattern changed when the researchers looked at the patient-divorce breakdown by sex. When the man became ill, only 3 percent experienced the end of a marriage. But among women, about 21 percent ended up separated or divorced. Among couples who split up, divorce occurred, on average, about six months after the diagnosis, although there was wide variability in the timing.

It is not known whether the illness prompted the breakup or whether the couples in the study who divorced were already experiencing marital problems before the diagnosis. If couples are happy before the diagnosis, it appears that men are more likely to abandon wives who become seriously ill. If couples are already troubled before a partner becomes ill, the finding suggests that women in unhappy marriages are less likely to proceed with a divorce if their husbands become ill.

“All these patients were couples when we met them, but we don’t know about pre-diagnosis marital conflicts that had been festering,” Dr. Chamberlain said. “But the striking part is with life-threatening illness, how often women are abandoned compared to men. That does not speak very well of my gender.”

Dr. Chamberlain speculated that differences in male and female roles in the family could explain the trend. “There clearly is an emotional attachment women have to spouse, family and home that in times of stress causes women to hunker down and deal with it, while men may want to flee,” he said.

Additional study is needed to understand why women appear more vulnerable to spousal abandonment after a diagnosis of serious illness. The study did find that couples who had been married longer were less likely to break up after a cancer diagnosis.

Hospitals and oncology practices may also want to consider including social workers and family therapists as part of a patient’s health care team, particularly for younger couples. Patients who lose spousal support after a cancer diagnosis are less likely to complete therapy or try new treatments. They have higher rates of hospitalization and lower rates of hospice care.

“It has an enormous impact,” Dr. Chamberlain said. “We know from other studies of patients with cancer that social support is so extremely important.”