People who were exposed to asbestos through a family member who worked with the material appear to run the risk of developing the asbestos-related cancer mesothelioma many years later, according to new research.

The study, based on a survey of law firms involved in asbestos claims, found 32 cases of mesothelioma diagnosed since 1990 among family members of workers exposed to asbestos. Wives and daughters were most often affected, with the lag time between asbestos exposure and cancer development topping 40 years in most cases.

Mesothelioma is a relatively rare cancer of the membrane that surrounds the internal organs, most often affecting the tissue that lines the chest cavity and protects the lungs.

The main cause of the cancer is exposure to airborne particles of asbestos, a fibrous mineral that was once widely used in insulation, fireproofing materials, tiles, brake pads and a host of other industrial products.

People with on-the-job exposure to asbestos - in industries such as construction, insulation manufacturing and shipbuilding - are at greatest risk of mesothelioma. The people who lived with them may also face an increased mesothelioma risk, because in the past these workers likely came home with particles of asbestos on their clothes and bodies.

For the new study, Dr. Albert Miller of St. Vincent Catholic Medical Center in New York obtained medical records and other data on asbestos claimants from 15 U.S. law firms. The findings are published in the May issue of the American Journal of Industrial Medicine.

Miller found 32 cases of mesothelioma diagnosed since 1990 that could be attributable only to “asbestos brought home by another resident of the household.” While most cases were seen in the wives or daughters of asbestos-exposed, a few cases occurred in sons and other relatives.

Six patients developed the cancer in their 40s, but the majority were age 60 or older when diagnosed, with the gap between asbestos exposure and diagnosis often surpassing 40 years.

Asbestos use has declined in the U.S., and people who still work with the material wear protective equipment. To cut the risk of bringing asbestos dust home, they are also typically required to shower and change clothes before leaving work.

Still, Miller notes in his report, the 32 mesothelioma cases in this study confirm the “ongoing risk” faced by family members with past asbestos exposure.

He also points out that while 90 percent of mesotheliomas in men have been attributed to asbestos, far fewer cases in women have been linked to the material. Miller speculates that many of these women with unexplained mesotheliomas may have lived with an asbestos-exposed worker at some point.

SOURCE: American Journal of Industrial Medicine, May 2005.