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After years of trying to pinpoint the cause of a brain cancer cluster at its Naperville research center, BP Amoco PLC announced Tuesday that it has settled five of six lawsuits brought on behalf of former employees stricken with the deadly disease.

Although medical researchers were at a loss to explain the illnesses, Amoco is avoiding what promised to be a prolonged court battle by settling the cases.

The five lawsuits are expected to be dismissed Wednesday, and the oil giant said it is confident that the sixth also will be settled and dismissed. But Amoco still faces a raft of litigation related to other types of tumors contracted by former Naperville employees.

Neither the company nor attorneys for the employees who settled would disclose the amounts of their agreements.

“They are fair amounts for all the families concerned,” said attorney Marios Karayannis, whose father, Nicholas, died of a glioma, the rare, malignant brain tumor common to all six workers at the Naperville center.

“Money doesn’t pay for your husband’s life, and that’s all I’ve got to say,” said Karayannis’ widow, Sasha, reached Tuesday.

Nicholas Karayannis and five other Amoco employees worked in the research center’s Building 503 during the same period in the late 1970s and early ’80s.

They all were white, male, long-term employees of Amoco, averaging 17 years in tenure, compared with the average of nine years among Naperville employees altogether. Five of the six men worked on the third floor, which now has been closed.

Last year, researchers from the University of Alabama-Birmingham and Johns Hopkins University concluded that the six cases were more likely than not workplace related.

“They did find a consistent pattern that indicated the glioma may be work related,” said Amoco spokeswoman Vicki Kastory. “While we still don’t have specific, conclusive answers about what specifically caused the cancer, there is a consistent pattern. Our philosophy from the beginning has been to address these concerns, and it’s only the right thing to resolve these issues.”

Amoco spent millions of dollars on the research study looking into the strange incidence of cancer at the site, winning plaudits from workplace activists for its proactive approach.

The study was considered unprecedented, and was expected to encourage other companies to investigate their workplaces. On-the-job exposures are believed to account for up to 10 percent of all cancers.

In addition to the lawsuits brought by the six brain cancer victims, other suits have been filed related to the pattern of illness at Naperville, but Amoco has not settled those claims.

The university researchers concluded that 13 other tumors among former employees showed no pattern linked to the job.

Besides the settlement with Karayannis, Amoco said Tuesday it also reached agreements with Glen Hoff, who was diagnosed in 1989 and is alive; and the estates of David Palmer, diagnosed in 1986, who died in 1997; Cecil Bergman, diagnosed in 1989, who died in 1994; and David Brady of St. Charles, diagnosed in 1998, who died last year, plaintiffs’ lawyers confirmed.

A sixth case has not been settled yet. But Amoco officials said they expect to settle it. A source close to the case said the plaintiff in that case is Walter Kus of Naperville, who was diagnosed in 1997 and died in 1998.

The wife of the only living plaintiff, reached Tuesday at the couple’s Provo, Utah, home, said she is relieved about the settlement. But her husband is very ill, she said.

“He has gone downhill and has suffered many strokes in the last year that have made him wheelchair-bound,” said Janet Hoff, wife of Glen Hoff, 57. “Right now he is on a level plane. He is at home and he can talk, though it is not always the best conversation.”

Hoff had mixed feelings about her family’s experiences with the oil company. “I am glad the settlement is over and I can’t say Amoco was nasty,” she said. “They tried to accommodate us during the study. I think they did a good job and our lawyers did a good job. But I would rather have no money at all and have his life. He has only one life.” The Hoffs, who have four grown children, have been living in Provo more than two years.

In the research study, investigators focused on some tantalizing clues. The six glioma victims, they found, were more frequent users than their workplace colleagues of a chemical called n-hexane used to make plastics. They also were more frequently involved in a process involving ionizing radiation used to track compounds in chemical reactions.

The researchers concluded that neither alone was the culprit in the glioma cases. Amoco said it would continue to search.