ADJ11687715 · September 24, 2026

The Appeals Board agreed with the WCJ that the expert opinion of PQME Dr. Lonky constituted substantial medical evidence that the decedent's lung cancer and death were industrially caused by diesel exhaust exposure as a co-carcinogen, even with the decedent's smoking history, meeting the burden of proof by reasonable probability.

From the decision · page 4The Court held that the uncontroverted evidence established exposure to smoke, the doctor stated that it was probable that the smoke inhaled contained carcinogens and it was reason that prolonged exposure could lead to lung cancer, need only establish that it was reasonably probable and was not required to produce exact type/amount of exposure, and that employment need only be a contributing cause. In the present matter, the issue of AOE/COE was addressed in the Findings of Fact. Applicant alleged that the decedent’s lung cancer and resulting death were caused by diesel exhaust exposure at work. The parties used Stuart Lonky, MD as the panel qualified medical evaluator. QME Lonky provided five reports and sat for four depositions. He reviewed extensive medical records, deposition transcripts from various employees at the City of Sacramento, including the Kristal the applicant, the injured worker’s spouse, and multiple medical articles on the relationship between diesel fumes and lung cancer. Throughout the reporting and deposition testimony, QME Lonky opined that there was industrial causation. QME Lonky’s

Decedent was exposed to diesel exhaust in the workplace, which is a known carcinogen.

Favours Applicant prevailed

This exposure was found to be a contributing cause of the decedent's lung cancer and death, supporting industrial causation.

From the decision · page 7Applicant demonstrated that there was diesel exhaust exposure in the workplace. The evidence showed that the decedent operated vehicles that used diesel fuel. The diesel fuel that the decedent was exposed to is well-known carcinogen (Applicant Exhibit 11 and Joint Exhibit 2, page 27). QME Lonky explained through multiple reports and depositions that the diesel exhaust exposure was a co-carcinogen even though exposure was low level and intermittent. Per McAllister, Applicant does not need to show the exact type/amount of exposure with scientific certainty, only reasonable probability.

PQME Dr. Lonky opined that diesel exhaust acted as a co-carcinogen contributing at least 1% to the development of lung cancer despite the decedent's smoking history.

Favours Applicant prevailed

The Board found this expert opinion to be substantial medical evidence supporting causation, meeting the burden of proof by reasonable probability.

From the decision · page 4The Court held that the uncontroverted evidence established exposure to smoke, the doctor stated that it was probable that the smoke inhaled contained carcinogens and it was reason that prolonged exposure could lead to lung cancer, need only establish that it was reasonably probable and was not required to produce exact type/amount of exposure, and that employment need only be a contributing cause. In the present matter, the issue of AOE/COE was addressed in the Findings of Fact. Applicant alleged that the decedent’s lung cancer and resulting death were caused by diesel exhaust exposure at work. The parties used Stuart Lonky, MD as the panel qualified medical evaluator. QME Lonky provided five reports and sat for four depositions. He reviewed extensive medical records, deposition transcripts from various employees at the City of Sacramento, including the Kristal the applicant, the injured worker’s spouse, and multiple medical articles on the relationship between diesel fumes and lung cancer. Throughout the reporting and deposition testimony, QME Lonky opined that there was industrial causation. QME Lonky’s

Dr. Lonky opined that the decedent's lung cancer and death were industrially caused by diesel exhaust exposure acting as a co-carcinogen, contributing at least 1% to the development of cancer despite the decedent's smoking history, and that this opinion constituted substantial medical evidence supporting causation.

Dr. Lonky reviewed extensive medical records, depositions, and medical literature, and consistently maintained his opinion despite defense questioning, explaining the role of diesel exhaust as a co-carcinogen accelerating cancer development.

From the decision · page 4The Court held that the uncontroverted evidence established exposure to smoke, the doctor stated that it was probable that the smoke inhaled contained carcinogens and it was reason that prolonged exposure could lead to lung cancer, need only establish that it was reasonably probable and was not required to produce exact type/amount of exposure, and that employment need only be a contributing cause. In the present matter, the issue of AOE/COE was addressed in the Findings of Fact. Applicant alleged that the decedent’s lung cancer and resulting death were caused by diesel exhaust exposure at work. The parties used Stuart Lonky, MD as the panel qualified medical evaluator. QME Lonky provided five reports and sat for four depositions. He reviewed extensive medical records, deposition transcripts from various employees at the City of Sacramento, including the Kristal the applicant, the injured worker’s spouse, and multiple medical articles on the relationship between diesel fumes and lung cancer. Throughout the reporting and deposition testimony, QME Lonky opined that there was industrial causation. QME Lonky’s

South Coast Framing v. Workers’ Comp. Appeals Bd. (Clark) (2015) 61 Cal.4th 291

The injured worker must prove by a preponderance of the evidence that an injury arises out of and occurs in the course of employment (Labor Code §§ 3202.5, 3600(a)).

The Board applied this standard to find that the decedent's lung cancer and death were industrially caused by employment exposure to diesel exhaust as a co-carcinogen.

From the decision · page 4When an injured worker claims a physical injury, the injured worker has the initial burden of proving industrial causation by showing the employment was a contributing cause. (South Coast Framing v. Workers’ Comp. Appeals Bd. (Clark) (2015) 61 Cal.4th 291, 297-298, 302; § 5705.) The injured worker must prove by a preponderance of the evidence that an injury arises out of and occurs in the course of employment (Labor Code §§ 3202.5, 3600(a)). “The requirement of Labor Code section 3600 is twofold. On the one hand, the injury must occur in the course of the employment. This concept ordinarily refers to the time, place, and circumstances under which the injury occurs. On the other hand, the statute requires that an injury arise out of the employment. It has long been settled that for an injury to arise out of the employment it must occur by reason of a condition or incident of the employment. That is, the employment and the injury must be linked in some causal fashion. *** The statutory proximate cause language [of section 3600] has been held to be less restrictive than that used in tort law, because of the statutory policy set forth in the Labor Code favoring awards of employee benefits.

McAllister v. Workers’ Comp. Appeals Bd. (1968) 69 Cal.2d 408

Causation may be found on reasonable probability even where the exact mechanism is unclear; employment need only be a contributing cause (McAllister v. Workers’ Comp. Appeals Bd. (1968) 69 Cal.2d 408).

The Board relied on this precedent to uphold the finding of industrial causation despite the decedent's smoking history and the presence of other carcinogens, emphasizing reasonable medical probability rather than scientific certainty.

From the decision · page 4In general, for the purposes of the causation requirement in workers’ compensation, it is sufficient if the connection between work and the injury be a contributing cause of the injury.” (South Coast Framing, supra at 297-298 (internal citations and quotations omitted).) Furthermore, the California Supreme Court has held that causation may be found on reasonable probability even where the exact mechanism is unclear, the Board cannot demand an “unbearable” level of specificity about toxicity and quality of exposure as though scientific certainty were required. Employment need only to be a “contributing cause” of injury (McAllister v. Workers’ Comp. Appeals Bd. (1968) 69 Cal.2d 408). McAllister involved the death of a fireman after toxic exposure to smoke.

Expert medical opinion of PQME Dr. Lonky that diesel exhaust exposure acted as a co-carcinogen contributing to lung cancer causation despite low level and intermittent exposure.

From the decision · page 7(1974) 11 Cal.3d 274 [39 Cal.Comp.Cases 310]; Garza v. Workmen’s Comp. Appeals Bd. (1970) 3 Cal.3d 312 [35 Cal.Comp.Cases 500]; LeVesque v. Workmen’s Comp. Appeals Bd. (1970) 1 Cal.3d 627 [35 Cal.Comp.Cases 16].) “The term ‘substantial evidence’ means evidence which, if true, has probative force on the issues. It is more than a mere scintilla, and means such relevant evidence as a reasonable mind might accept as adequate to support a conclusion…It must be reasonable in nature, credible, and of solid value.” (Braewood Convalescent Hospital v. Workers’ Comp. Appeals Bd. (Bolton) (1983) 34 Cal.3d 159, 164 [48 Cal.Comp.Cases 566], emphasis removed and citations omitted.) We agree with the WCJ that the expert opinion of Dr. Lonky on causation constitutes substantial medical evidence. The PQME’s reasoning that decedent’s proven exposure to diesel exhaust in the workplace provided a co-carcinogen that contributed to the causation of lung cancer to some degree, however miniscule, has probative value and is reasonable in nature. It is more than a mere scintilla of evidence, and is not pure conjecture, even though the workplace exposure to diesel exhaust was low level and intermittent. Defendant’s contention that the PQME’s opinion