State regulators will examine a shuttered manufacturing plant as a possible source of environmental contaminants that may be behind an outbreak of tumors among northwest Missouri residents.

The Rockwool Industries plant three miles west of Cameron produced fiber insulation before closing more than two decades ago. The city then bought the building and leased it from 1992 to 2003 to Midwest Hanger, a Kansas City coat hanger manufacturer.

State environmental health officials disclosed the plan this week at a hearing attended by more than 150 worried residents. Local activists have identified 11 area residents who have become afflicted with tumors since 2002.

The number could be much higher. After initially declining to disclose the number of tumor reports submitted, two officials who oversee the state's cancer registry said they have received between 20 and 40 reports indicating similar problems from area residents.

 They cautioned that those reports are not yet verified. And the state has tracked only benign, nonmalignant brain tumors since 2004, making historical comparisons and causal conclusions difficult.

"We are not going to be able to calculate a rate when we get (complete data) because we don't have anything to compare it to," said Jeannette Jackson-Thompson, operations director for the Missouri Cancer Registry.

Among those at the meeting was Billy Kemper, whose 44-year-old wife, Karen, died from complications caused by a tumor-related stroke in May, just one month after her diagnosis.

"She thought she had an inner ear infection," he said. "She had an MRI and that's when they discovered the brain tumor."

Tests by the Missouri Department of Natural Resources ruled out the city's water supply as a likely cause.

"Nothing was found in the water above the (acceptable) standard," said Cheri Baysinger, a Department of Health and Senior Services epidemiologist.

The absence of answers frustrated many audience members, even as state officials pledged their support.

"We'll do whatever we need to get to the bottom of this," Jackson-Thompson said.

Environmental tests of the manufacturing site should begin in several weeks, regulators said. Another community meeting will be held once those results are available.

Cameron resident Jim Frasher, whose doctor found a benign tumor about the size of a golf ball on his brain stem in January, compiled a list of 11 area residents - four women and seven men - who developed tumors between 2002 and 2008.

Seven of those were identified in the last two years. The victims' ages range from a 6-year-old boy to the 61-year-old Frasher. All but one of the tumors were found in the brain.

The range of ages and the split between benign and malignant tumors make it unlikely that a single cause may be found, according to cancer experts.