Town of Castle Rock & Cirsa v. Industrial Claim Appeals Office, 2013 COA 109

Claimant Mike Zukowski, a firefighter with the Town of Castle Rock since 2000, was diagnosed with malignant melanoma in 2011 after >5 years of service.
Section 8-41-209 creates a rebuttable presumption that specified cancers in firefighters with ≥5 years’ service are occupational; the employer can rebut by proving "by a preponderance of the medical evidence" the cancer "did not occur on the job."
The Town retained Dr. Milliken (occupational/environmental medicine), who concluded claimant’s melanoma was far more likely caused by non-occupational risks (significant UV exposure and multiple/atypical nevi) than by firefighting (estimated relative risk from firefighting ≈1.32 vs. much higher risks from nevi and sun).
Claimant’s expert (Dr. Mayer) agreed on the relative-risk statistics and that the specific causative exposure could not be known, but emphasized that relative risk ≠ definitive causation.
The ALJ held the Town failed to rebut the presumption because the Town did not identify a specific non-work cause; the ICAP affirmed.
The court reversed: evidence showing an alternative probable cause (risk evidence making non-occupational cause more likely than occupational cause) can satisfy the statutory preponderance standard and rebut the presumption. Remanded for application of that standard.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether an employer must prove a specific non-work cause to rebut § 8-41-209(2)(b) presumption	Claimant: employer must show cancer "did not occur on the job" only if specific non-work cause proven; statistical/relative-risk proof insufficient	Town: statute requires only preponderance of medical evidence that the cancer did not occur on the job; risk-based evidence showing an alternative source is more probable suffices	Court: Employer need not identify a singular specific cause; risk-evidence that a non-work source is more likely than occupational exposure can rebut the presumption (preponderance standard).
Whether the Town’s risk-evidence was sufficient under the correct standard	Claimant: relative-risk testimony does not prove the cancer did not occur at work; ALJ found Town’s evidence insufficient	Town: Dr. Milliken’s and corroborating evidence showed non-occupational risks more likely caused melanoma	Remanded: ALJ must reassess whether, by a preponderance of medical evidence, it is more probable than not that claimant’s melanoma did not occur on the job using the correct (probability-based) standard.

Davison v. Indus. Claim Appeals Office, 84 P.3d 1023 (Colo. 2004) (interpret statutes by plain meaning).
Support, Inc. v. Indus. Claim Appeals Office, 968 P.2d 174 (Colo. App. 1998) (agency interpretation set aside if inconsistent with statute/legislative intent).
Schocke v. State, 719 P.2d 361 (Colo. App. 1986) (explaining preponderance standard: even weight resolves against party with burden).
Olivas-Soto v. Indus. Claim Appeals Office, 143 P.3d 1178 (Colo. App. 2006) (deference to Panel’s interpretations limited).
Elter v. North Dakota Workers Comp. Bureau, 599 N.W.2d 315 (N.D. 1999) (alternative probable cause can rebut occupational presumption).
Byous v. Missouri Local Gov't Emps. Ret. Sys. Bd. of Trs., 157 S.W.3d 740 (Mo. Ct. App. 2005) (employer may rebut presumption by showing non-work causes more probably caused condition).