1999-10-21 04:00:00 PDT NEW YORK -- Ruth had undergone a mysterious personality change that defied psychiatric explanation. Charles awoke each morning with a severe headache that eased as the day progressed. Kathleen experienced partial facial paralysis, slurred her words and drooled. Marlys suffered a grand mal seizure that rendered her unconscious for about 15 minutes.

All four had different kinds of brain tumors. Ruth's was benign and grew slowly, but it was not detected for years -- too late for treatment that could have saved her.

Charles' tumor was malignant, and despite the best therapy available at the time, he succumbed to primary brain cancer within two years.

Kathleen's tumor was also malignant, but it had not started in the brain. Rather, it resulted from the spread of a lung cancer that ultimately took her life.

Marlys was the lucky one. Her benign tumor was detected by modern imaging while it was small and in an area that permitted surgical removal without any harm.

For reasons yet to be determined, brain tumors are becoming more common, especially in older people. The latest well-known victim is Cardinal John O'Connor, archbishop of New York, whose small tumor was surgically removed this month at Memorial Sloan-Kettering Cancer Center in New York. Although the nature of the tumor has not been revealed, O'Connor, 79, will be undergoing several weeks of radiation therapy, which is typically used to prevent the spread of cancer from cells that may have escaped the surgeon's scalpel.

Since the mid-1980s, the yearly total of Americans given diagnoses of brain tumors has doubled, and it is expected to exceed 100,000 this year. More than half the increase has occurred in people over age 65.

Survival rates, too, have been inching up, thanks to improved diagnostic techniques and more precise and inventive treatments like stereotactic radiosurgery (a pinpoint form of radiation) and laser surgery with a gamma knife. More progress is expected to result from some still experimental treatments, including immunotherapy, gene therapy and implanted wafers of chemotherapeutic agents.

Only about 20 percent of brain tumors are primary -- that is, tumors that start in brain tissue. Half of these are brain cancers, and half are benign tumors that can, nonetheless, become life threatening because they grow inside a skull that cannot expand. As they do, they can press on vital tissues, which may sometimes preclude their removal.

The remaining 80 percent of brain tumors are secondary, originating from cancers elsewhere in the body -- although, as in Kathleen's case, the primary cancer is sometimes not detected until after the metastatic brain tumor has been found. Lung, breast and colon cancers, as well as melanomas, often spread to the brain.

There has been much speculation about the possible causes of brain cancers, and especially their apparent increase. About 5 percent are hereditary. Among suggested environmental factors are low-energy electromagnetic fields from objects like cellular phones, power lines and household appliances, although considerable research into the matter has yet to yield any definitive evidence of such a risk. To be sure, high-dose radiation delivered to the head, including therapy for brain tumors, can increase the risk of brain cancer. There is no link, however, to low-dose radiation delivered through diagnostic X-rays or workplace exposure to ionizing radiation.

But industrial chemicals may be a problem. Workers regularly exposed to substances like acrylonitrite, vinyl chloride, formaldehyde, lubricating oils, N-nitroso compounds, phenols, pesticides, polycyclic aromatic hydrocarbons and organic solvents develop brain tumors with greater than average frequency. Pregnant women and parents of infants should be especially careful to avoid such chemicals because animal studies indicate that exposure in utero and in infancy incurs the greatest risk.

Also, pregnant women would be wise to take supplements containing vitamins C, A, E and folate through their pregnancies. A three- continent study indicated that the children of women who took such vitamins were half as likely as the children of nontakers to develop brain tumors before age 5.

Benign brain tumors can often be treated successfully, although there may be lasting effects, depending on size and location. But because the most common type of brain cancer, glioblastoma multiforme, is fast- growing and highly invasive, and because early symptoms of brain tumors often mimic other problems, delaying diagnosis, brain cancer is associated with a five-year survival rate of only 30 percent. This rate is half that for cancers overall, but still much better than the survival rates for cancers of the lung, pancreas and esophagus.

The problem with brain tumors is their ability to grow silently for years. When they finally do produce symptoms, they become confused with other problems like migraine headaches, inner ear problems, epilepsy or stroke. For example, Kathleen, who had speech problems and drooling, thought at first she might have had a stroke.

If everyone with symptoms like headache, dizziness, nausea, vomiting, memory loss, personality or behavioral change, hearing problems, difficulty walking, decreased sensation, seizures or blurred or double vision underwent a thorough workup for a brain tumor, it could easily overwhelm the health care system. But if such symptoms persist or keep recurring, patients should insist on being examined for possible brain tumors.

The treatment of choice depends on the patient's age (children under 3 are generally not given radiation therapy), the size and location of the tumor, the sensitivity of the tumor to radiation and chemotherapy, and the general health of the patient. The three common cancer treatments -- surgery, radiation therapy and chemotherapy -- are most often used for brain tumors as well. But there are now highly sophisticated ways of operating on the brain, including the use of pinpoint radiation and laser beams.