State Supreme Court Holds Causation Evidence Insufficient

The Vermont Supreme Court recently held that a plaintiff's evidence that exposure to benzene allegedly caused his cancer was insufficient to get to the jury.  Blanchard v. Goodyear Tire & Rubber Co.,  No. 2010-250 (Vt. 8/5/11).

Plaintiff was diagnosed with non-Hodgkin's lymphoma, and he attributed the onset of the disease to benzene exposure that allegedly occurred between 1968 and 1973 while he was a teenager playing on a ball field on the grounds of the former Goodyear rubber manufacturing plant. That  plant operated in Windsor, Vermont from 1936 to 1986. He sued, alleging that the field itself was polluted and that there was a gully in the outfield that transported foul-smelling and oily stormwater discharge away from the manufacturing plant.

Defendants moved for summary judgment. The lower court concluded that plaintiff was not entitled to present his case to a jury because he had provided insufficient evidence to support an inference that he had been exposed to benzene in any amount, let alone an amount that could have caused his illness, nor sufficient expert testimony sufficient to eliminate other potential causes of his disease. On appeal, plaintiff argued that his circumstantial evidence of causation was sufficient to present his case to the jury.

The state Supreme Court noted that the plaintiff could not survive the motion for summary judgment on his toxic tort claim unless he was able to point to evidence suggesting a probability, rather than a mere possibility, that (1) he was exposed to the specified chemical at a level that could have caused his physical condition (general causation); and (2) the exposure to that chemical did in fact result in the condition (specific causation).  In a toxic tort case, general causation addresses whether a substance is capable of causing a particular injury or condition in a population, while specific causation addresses whether a substance caused a particular individual's alleged injury. E.g., King v. Burlington Northern Santa Fe Ry. Co., 762 N.W.2d 24, 34 (Neb. 2009). General causation is typically shown through epidemiological studies, and plaintiffs in toxic exposure cases in Vermont generally must demonstrate specific causation by submitting evidence concerning the amount, duration, intensity, and frequency of exposure. Citing  Henricksen v. ConocoPhillips Co., 605 F. Supp. 2d 1142, 1157 (E.D. Wash. 2009) (citing several appellate court cases holding that experts testifying as to specific causation must pay careful attention to amount, intensity, and duration of exposure).

The court recognized that in some toxic tort cases it is impossible to quantify exposure with hard proof, such as the presence of the alleged toxic substance in the plaintiff's blood or tissue and the precise amount of the toxic substance to which an individual plaintiff was exposed. Plourde v. Gladstone, 190 F. Supp. 2d 708, 721 (D. Vt. 2002).  Therefore, expert testimony on toxic injuries may be admissible where dosage or exposure levels have been established through sufficient reliable circumstantial evidence. While it is not always necessary for a plaintiff to quantify exposure levels precisely, the courts generally preclude experts from testifying as to specific causation without having any some measurement or reasonable estimate of a  plaintiff's exposure to the allegedly harmful substance. Finally, a defendant's concession that its product contains a carcinogen, say benzene, does not excuse a plaintiff from having to show the benzene contained in defendant's product is capable of causing the illness at issue.

When direct evidence of the precise amount of exposure to a toxic substance is limited, some courts have allowed expert witnesses to use a differential diagnosis process as a method of proving specific causation. We have posted before about the mis-use and mischaracterization of this process.  Differential diagnosis is a scientific analysis entailing the weighing of relevant evidence, listing all likely explanations of the patient's observed symptoms or injury, then eliminating all but one.  Some courts have made the leap from allowing the process designed to arrive at a diagnosis (what disease caused the symptoms) to arrive at a cause (what substance caused the disease). However, said the state court, even the courts that do recognize differential diagnosis are reluctant to admit causation testimony based on a differential diagnosis where the proffered expert possesses only weak circumstantial evidence that some exposure occurred and makes insufficient effort to scientifically evaluate or estimate the degree of exposure or dosage. Also, and significantly, standing alone, the presence of a known risk factor is not a sufficient basis for ruling out idiopathic origin in a particular case, particularly where most cases of the disease have no known cause. In such cases, analysis beyond a differential diagnosis is required.

Here, plaintiff pointed to three bits of circumstantial evidence. First, he offered statements made by himself and boyhood friends concerning their alleged exposure to chemicals from the Goodyear plant when they were teenagers playing ball on a field adjoining the plant.  Second, plaintiff relied on the testimony of the project manager for an environmental firm hired by Goodyear in 2007 to conduct a site investigation in response to a clean-up agreement reached by Goodyear and the State of Vermont. The 2009 report stemming from the investigation listed contaminants of concern, including petroleum products containing benzene, that could have been released into the environment. Third, plaintiff relies upon the testimony of his two experts, who testified that occupational exposure to benzene is generally associated with a risk of non-Hodgkin's lymphoma, and that plaintiff's cancer was not caused by an immunodeficiency disorder, one of the known causes of that form of cancer.

That evidence "falls well short" of what plaintiff would be required to show in order to prevail in a jury trial. Indeed, if a jury were to find in favor of plaintiff on the evidence relied upon by plaintiff, said the court, "we would have to overturn the verdict." In the end, plaintiff's suspicion that his cancer was caused by exposure to benzene on the Goodyear ball field when he was a teenager was purely speculative. There was no way to know whether any benzene-containing product actually contaminated the ball field.  And there was no evidence indicating the amount or concentration of benzene that was present, even assuming some was. Nor was there any evidence indicating plaintiff's level of exposure to any benzene that may have been present on the field. Nor was plaintiff able to point to studies indicating a risk of cancer posed by exposure to limited amounts of benzene from petroleum products in an outside environment.  

Further, plaintiff could not rely upon differential diagnosis to overcome the complete lack of evidence as to the level of any exposure to benzene. A large percentage of cases of plaintiff's type of lymphoma are of unknown origin. Thus plaintiff's experts could not rule out all other causes, an essential part of the differential diagnosis.  E.g., Whiting v. Boston Edison Co., 891 F. Supp. 12, 21 n.41 (D. Mass. 1995) (concluding that differential diagnosis cannot be used to explain disease where 90% of cases of disease are of unknown origin).
 

Appeals Court Upholds Summary Judgment Based on Daubert in Benzene Case

The Sixth Circuit last week upheld the dismissal of a plaintiff''s claim that benzene exposure caused her cancer. Pluck v. BP Oil Pipeline Co., No. 09-4572 (6th Cir.,  5/12/11).  The central issue was the exclusion of plaintiff's causation expert's opinion based on a "differential diagnosis" that failed to reliably rule in benzene exposure as a potential cause of plaintiff's cancer, and to rule out some other potential exposures.

This case arose from benzene contamination allegedly caused by gas-pipeline releases allegedly resulting in the seepage of gasoline into the surrounding soil and groundwater. Benzene, a component of gasoline, is a known carcinogen in sufficient doses under certain exposure circumstances, and is also ubiquitous in the ambient air and is a component or constituent of vehicle exhaust and cigarette smoke, said the court. Plaintiffs purchased a home in the area,  and used well water to drink, wash, shower, and irrigate their yard and garden. In October,  1996, plaintiffs say they noticed a gasoline odor in their home and water, and benzene was first detected in the well on their property in the amount of 3.6 parts per billion (“ppb”).  They began drinking bottled water in lieu of tap water, although they claim to have resumed drinking tap water upon the drilling of a new, deeper well. Between 1997 and May 2002, the new well tested negative for benzene twenty-two times.

Mrs. Pluck was diagnosed with Non-Hodgkins lymphoma (“NHL”) in 2002 at age forty-eight. She filed suit, alleging claims of strict liability for hazardous activity, negligence, and loss of consortium. To support their claims, plaintiff and spouse retained Drs. Joseph Landolph and James Dahlgren as experts on causation to demonstrate that benzene is generally capable of causing NHL and specifically caused Mrs. Pluck’s NHL. Defendant filed motions in limine to exclude the testimony of Dahlgren and Landolph on the grounds that their testimony failed to satisfy the standard for reliability set forth in Daubert. In particular, BP argued that Dr. Dahlgren’s testimony on specific causation was unreliable because he formulated a specific causation opinion without evidence of dose, and subsequently performed an unreliable dose reconstruction in an attempt to support his opinion.  Dahlgren then submitted a supplemental declaration in which he evaluated Mrs. Pluck’s illness under a "differential-diagnosis" methodology. The district court granted the motions, and plaintiff appealed.

In a toxic tort case, as here, the plaintiff must establish both general and specific causation through proof that the toxic substance is capable of causing, and did cause, the plaintiff’s alleged injury.  As to specific causation, the plaintiff must show that she was exposed to the toxic substance and that the level of exposure was sufficient to induce the complained-of medical condition (based on a dose-response relationship). Both causation inquiries involve scientific assessments that must be established through the testimony of a medical expert. Without this testimony, a plaintiff’s toxic tort claim will fail.

The Plucks had to concede that the expert Dr. Dahlgren did not establish dose; they instead argued that Dahlgren used differential diagnosis to determine specific causation. Defendant argued that Dr. Dahlgren did not apply differential diagnosis in either his expert opinion or his deposition, but did so only in an untimely supplemental declaration filed five months after the deadline for expert reports. And in any event, his approach was flawed. The Sixth Circuit has recognized differential diagnosis, properly done, as an appropriate method for making a determination of causation for an individual instance of disease. Differential diagnosis -- originally a standard technique for determining what disease caused a patient's symptoms -- has been adapted in some courts as an acceptable scientific technique for identifying the cause of a medical problem by eliminating the likely causes until the most probable one is isolated. A physician who applies differential diagnosis to determine causation considers all ("rules in") relevant potential causes of the symptoms and then eliminates ("rules out") alternative causes based on a physical examination, clinical tests, and a thorough case history.

Even in courts that accept this adapted method, not every opinion that is reached via a differential-diagnosis method will meet the standard of reliability required by Daubert.  Calling something a “differential diagnosis” or “differential etiology” does not by itself answer the reliability question but prompts at least three more:

(1) Did the expert make an accurate diagnosis of the nature of the disease?

(2) Did the expert reliably rule in the possible causes of it?

(3) Did the expert reliably rule out the rejected causes?

If the court answers “no” to any of these questions, the court must exclude the ultimate conclusion reached.

Here the court agreed that Dahlgren could not reliably “rule in” benzene exposure as the cause of Mrs. Pluck’s NHL. In recognition of the fact that benzene poses a health concern at certain levels of exposure, the EPA has stated that the maximum permissible contaminant level for benzene in
drinking water is 5 ppb. 40 C.F.R. § 141.61(a)(2). Dahlgren, however, did not ascertain Mrs. Pluck’s level of benzene exposure, nor did he determine even whether she was exposed to quantities of benzene exceeding the EPA’s safety regulations. The levels of benzene in the Plucks’ wells never exceeded the maximum permissible contaminant level of 5 ppb designated by the EPA.

Dahlgren’s opinion that Mrs. Pluck’s “low-level exposure” to benzene caused her NHL was thus not grounded in “sufficient facts or data,”  nor did it reflect the “reliable principles and methods” required by Rule 702. It was, instead, pure conjecture.  Although the Plucks argued that the district court required too much specificity regarding Mrs. Pluck’s dose, this argument was also without merit. The mere existence of a toxin in the environment is insufficient to establish causation without proof that the level of exposure incurred could cause the plaintiff’s symptoms. See also McClain v. Metabolife Int’l, Inc., 401 F.3d 1233, 1242 (11th Cir. 2005) (causation “requires not simply proof of exposure to the substance, but proof of enough exposure to cause the plaintiff’s specific illness”).

Finally, even if Dr. Dahlgren had properly “ruled in” benzene exposure as the cause plaintiff's NHL, he failed to “rule out” alternative causes of her illness, as is required under the differential-diagnosis methodology. See also Wills v. Amerada Hess Corp., 379 F.3d 32, 50 (2d Cir. 2004) (expert’s opinion suffered from a “fatal flaw” when he acknowledged that cigarettes and alcohol were risk factors for developing squamous-cell carcinoma but failed to account for these variables in concluding that decedent’s cancer was caused by exposure to toxic chemicals such as benzene and PAHs).  In this case, Dahlgren acknowledged in his deposition that Mrs. Pluck was
exposed to other sources of benzene, from her extensive smoking habit and from other organic solvents.  Yet, Dr. Dahlgren neither identified these other solvents nor determined Mrs. Pluck’s potential level of exposure to these other possible sources of benzene.Thus, Dahlgren failed to “rule out” alternative causes of Mrs. Pluck’s NHL.

The court of appeals determined that the district court did not abuse its discretion in concluding that the expert did not perform a reliable differential diagnosis.  And summary judgment properly followed.