A Wyoming oil rig worker failed to prove his cancer was caused by exposure to toxic chemicals at work, the state Supreme Court ruled on Friday.

Brent McMillan, who worked for Unit Drilling Co. from 2011 to 2013, was diagnosed with smoldering multiple myeloma, a type of cancer that invades white blood cells, in 2013. In 2015 he filed a workers compensation report of injury, claiming that a number of physical conditions including nerve demyelination, neuropathy and chronic pain were caused by the cancer, which his doctors said was caused by his exposure to toxic chemicals at work, according to documents in Brent McMillan v. State of Wyoming, ex rel. Department of Workforce Services, Workers' Compensation Division, filed in Cheyenne.

The claim was denied on the basis that Mr. McMillan “did not submit evidence establishing a causal connection between his injury and employment,” documents state.

In support of his claim, Mr. McMillan in 2018 submitted to the state Workers’ Compensation Commission hundreds of pages of medical records and deposition transcripts from three doctors whose opinions lined up with his assertion that chemical exposure caused his cancer. He testified that his medical condition related to the high concentration of different chemicals released into the air during drilling and fracking, noting that during his last year of employment two fracking rigs were located within 800 feet of his oil rig. He said workers on the fracking rig wore hazardous material suits and respirators.

 In its opposition, the Workers’ Compensation Division relied on Mr. McMillan's deposition transcript, “which revealed alternative sources of chemical exposure and possible explanations for some of his symptoms unrelated to his employment at Unit Drilling Company,” documents state.

The commission ultimately found that the medical evidence “lacked expertise” and “lacked foundation” in asserting the chemical-cancer connection.

The court focused on the timing of the cancer, which emerged not five to 30 years after exposure, as is “usually” the case, according to medical testimony. His work and personal history were also a factor, according to documents.

“The Commission found several alternative sources of chemical exposure in Mr. McMillan's background,” documents state. “Specifically, he ‘had worked at a polymer plant making glue bases and latex’ where he wore a hazardous material suit and chemical-resistant respirator. He ‘experienced one prior workers' compensation injury while working on a grass seed farm when he had an allergic reaction from inhaling grass seed dust while driving an open swather during the harvest.’ And, as noted above, the record reflected he had a history of smoking,” documents state.

In affirming, the state’s highest court unanimously ruled that Mr. McMillan’s medical experts failed to meet the bar in workers comp law on causation, writing that the “Commission did not err when it concluded Mr. McMillan's … evidence could not carry his heightened burden.”