A rare throat cancer appears to have a "significant association" with longtime occupancy of mobile homes, according to research conducted for the Environmental Protection Agency. The cancer is nasopharyngeal cancer, or a cancer of the part of the throat leading to the nose. Although rare, it is frequently fatal soon after diagnosis. Researchers who discovered the association are not yet ready to say that their chief suspect in the atmosphere of mobile homes, formaldehyde, causes the cancer. Their report advised "extreme caution" in interpretation.