Association between soft tissue sarcomas, malignant lymphomas, and phenoxy herbicides/chlorophenols: evidence from occupational cohort studies.

Some case-control studies have reported a significant association between occupational use of phenoxy herbicides and chlorophenols and soft-tissue sarcomas and malignant lymphomas. However, persons who spray or apply these substances are concomitantly exposed to other potentially carcinogenic chemicals and oncogenic viruses, which have been found or suspected to play a role in the etiology of these tumors. No study has thoroughly controlled for these other exposures, some of which have been shown to be independently associated with these tumors even after controlling for exposure to phenoxy acids or chlorophenols. On the other hand, it has been found that an observed risk from exposure to phenoxy herbicides disappeared on controlling for some of these concomitant exposures in the rare instance this was attempted. Also, on several occasions, an association has been observed with occupations in which exposure to phenoxys and chlorophenols may occur, but not with the compounds themselves. Accordingly, a detailed review of the evidence from occupational cohort studies was conducted, to see if it corroborates that from case-control studies. It was found that the evidence does not unequivocally incriminate phenoxys and chlorophenols as a cause of these tumors. The results obtained with cohort studies of sprayers and applicators do not corroborate the association reported among this occupational group, in case-control studies. It is possible that the suspected association may well be due, partly or wholly, to one or more of the other concomitant exposures. However, in view of the fact that the majority of the cohorts need further follow-up to be informative, it is concluded that further studies of these cohorts are required before it can be determined whether or not these tumors are caused by exposure to phenoxy acids and chlorophenols.