Assessment of colorectal cancer incidence among polypropylene pilot plant employees.

Our recent study reported a colorectal cancer excess among workers involved in the manufacture of polypropylene. To follow up on this finding, we initiated a study of colorectal cancer incidence among polypropylene pilot plant workers within the same company. The purpose of this investigation was to determine whether colorectal cancer incidence was elevated among workers who may have had exposures similar to those experienced on the commercial production unit. The study population included 183 employees who worked at least 6 months on either of two pilot plants. Overall, there were three observed colorectal cases v. 3.3 expected (standardized incidence ratio = 0.9, 90% confidence interval 0.3 to 2.3). Analyses for the process, mechanic, and laboratory subgroup showed rates consistent with expected values (3 observed, 2.8 expected; standardized incidence ratio = 1.1, 90% confidence interval 0.3 to 2.8). Analyses by duration of employment and latency did not show patterns consistent with the colorectal cancer excess previously reported. The likelihood of lower or different exposures on the pilot plant than would be found on commercial production units is discussed along with the need for studies of workers in other polypropylene manufacturing environments.