Cancer incidence among employees at a petrochemical research facility

This investigation evaluated cancer incidence among workers at a petrochemi cal research facility in Illinois. A cluster of brain cancer and other intr acranial tumors had occurred at the facility before the study began. The su bjects were 5641 people who had worked at the facility from 1970 through 19 96 and who had lived in Illinois at any time between 1986 and 1997. Data on cancer cases came primarily from the Illinois State Cancer Registry. Analy ses compared the 1986-to-1997 cancer incidence rates of employees with Illi nois general population rates. Subjects had 18% fewer than expected total c ancers (125 observed/153 expected cases; standardized incidence ratio [SIR] , 82; 95% confidence interval [CI], 68 to 98), which was primarily attribut ed to a large deficit of lung cancer (10/26; SIR, 39; CI, 19 to 72). Brain cancer was increased in the overall study group (6/2.7; SIR, 222; CI, 81 to 484). This excess was restricted to white men who were scientists or techn icians for one of the three companies at the facility (6/0.8; SIR, 750; CI, 275 to 1633); all cases in this group had worked in the "500 building comp lex" (6/0.6; SIR, 968; CI, 355 to 2106). Subjects also had an increased inc idence of thyroid cancer (7/2.6; SIR, 265; CI, 106 to 546) that was not con centrated in particular occupational or building groups. The brain cancer i ncidence patterns indicated that an unidentified occupational exposure migh t have been responsible for the excess. Chance, socioeconomic factors leadi ng to better case detection in facility employees than in the general popul ation, and confounding by potential nonoccupational risk factors are plausi ble explanations of the observed increase in thyroid cancer.