- Disablement (exposure)
- Evidence (epidemiological)
- Exposure (benzene)
- Leukemia (chronic lymphocytic)
A worker was diagnosed with chronic lymphocytic leukemia (CLL) in late 2000. He received ongoing treatment for 7 years but his condition worsened and he passed away in August 2007. The worker's estate appealed a decision of the ARO which denied entitlement for CLL, and found that it was not probable that the worker's workplace exposure significantly contributed to the worker's CLL.
The Panel determined the claim would be determined on a disablement basis. For entitlement to be established, the evidence must demonstrate, on a balance of probabilities, that occupational exposure was a significant contributing factor in the development of the worker's CLL. It was noted that epidemiological evidence is crucial in establishing whether a causal relationship between certain exposures and certain diseases exists (Decision No. 1696/19).The Panel found that there was limited evidence between CLL and benzene as a carcinogenic risk. Based on Canadian and Australian studies reviewed, it was found that there was no probable association between the two. In addition, there was no large study which suggested a RR of 2 or SMR of 200, which would establish a likely connection.The Panel noted that, with respect to disease latency, the worker's greatest risk would have come 10 years or more before the diagnosis in late 2000 (1990). The OHCOW report submitted by the worker's representative was authored 8 years after the worker attended at the clinic in 2007. The Panel found that the report submitted by the worker's representative likely overestimated the nature and extent of the worker's exposure over the course of his 27 year work history. It was also noted that when benzene became a designated substance in 1985, reliance on and use of it diminished accordingly.The Panel, however, pointed out that there were limitations to epidemiological studies when it came to adjudicating a single case. For instance, if the studies showed a SMR of 150 rather than 200, it could mean a certain number of participants did have a causal connection. Therefore, to conclude that a worker's CLL was related to benzene exposure when the epidemiological studies did not support that probability, there would have to be something about the worker's employment history that would allow one to conclude that his benzene exposure was greater or more intense than would be expected.The Panel found that this did not exist in this case. The samples taken from the employer demonstrated 0 ppm of benzene levels. As such, based on a balance of probabilities, the worker's benzene exposure in his workplace environment did not contribute to the development of his CLL.