Potential confounding facstors in cancer studies

I read the recent study¹ regarding prognostic factors for dogs living > 1 year after a diagnosis of osteosarcoma with interest. The authors reviewed medical records for 90 dogs that lived > 1 year after an initial diagnosis of osteosarcoma, and found that 12 of the 90 (13%) did not receive adjuvant chemotherapy following surgical removal of the primary tumor but still had a prolonged survival time. I suspect that many of these 12 dogs received herbs, supplements, or other therapies that may have contributed to their prolonged survival times.

Use of complementary and alternative medical therapies is fairly widespread among pet owners. In a survey of owners of dogs and cats with cancer, for instance, Lana et al² found that 76% of the owners reported some use of complementary and alternative medical therapies, with nutritional supplements being the most commonly used therapy. Preliminary studies^3,4 on canine cancer cell lines in general and other studies^5,6 on canine osteosarcoma cell lines specifically indicated that supplementation of natural compounds may inhibit cancer cell growth.

The likelihood of supplementation and its effects should be taken into consideration in future cancer studies, and failure to do so should be acknowledged in the discussion of the research. The study of complete information regarding what therapies are actually being applied to cancer patients may help improve our understanding of cancer treatment.

Douglas Knueven, dvm

Beaver Animal Clinic Beaver, Pa

Supports anesthesia for veterinary dental cleanings

I read the recent letters in support of nonanesthetic dental cleaning in dogs with interest.^1,2 However, I strongly believe that a complete assessment of oral health and a full dental cleaning, including not just scaling (especially subgingival scaling) but also probing and polishing, cannot be performed appropriately in most dogs without anesthesia. The potential trauma that can result from performing these procedures in awake dogs and the potential to miss subgingival lesions³ have been documented.

The argument that nonanesthetic dental cleanings should be offered in veterinary medicine because that is how dental cleanings are typically performed in humans is, to me, invalid. I too have my teeth cleaned without anesthesia. However, I do not bite or claw my dentist or attempt to escape during uncomfortable parts of the procedure. I don't have any dental lesions and still do not enjoy undergoing scaling and probing. I can only imagine how this would feel if substantial periodontal disease were present.

I agree that anesthesia is not a risk-free procedure and its use should not be taken lightly. That risk is minimized, however, when tailored protocols and careful, consistent monitoring are in place. One study⁴ found that the risk of death in healthy small animal patients undergoing anesthesia was approximately 0.1% to 0.2%. In the case of periodontal disease, I believe that the benefits of anesthesia outweigh the risks.

In my opinion, the most compelling argument against nonanesthetic dental cleanings in companion animals is that experts in veterinary dentistry do not support their use.⁵ When the most knowledgeable and experienced people in a particular area uniformly argue against a particular procedure, it is likely with good reason. Perhaps we should listen.

Thomas Hansen, dvm

Walnut Creek, Calif

Lead ammunition

The recent commentary on lead ammunition and fishing gear¹ raises some important issues. When I was director of a diagnostic laboratory, placement of sporting clay courses on the periphery of corn fields became popular, and I saw a number of cases of lead toxicosis involving cattle fed corn silage harvested from these fields. Affected animals had a wide range of clinical signs; however, I was aware of only 2 animals that died after developing signs of lead toxicosis. Herdmates had few clinical signs but were, on the other hand, producing milk and meat containing lead. The danger to individuals who ingested food products from these cattle is obvious.^2,3

Waterfowl scavenging in grain fields after the harvest can ingest lead shot from contaminated fields. A single round of sporting clays with 50 shooters each firing at 50 targets can result in some 2,500 ounces of lead shot spread over the firing range. Although there is little doubt that nonlead shot should be used at such events, my experience suggests that much less lead shot is used when hunting live game, with fewer attributable cases of lead toxicosis.

I have read of the dangers of lead fishing tackle to waterfowl and raptors, but I have never made a diagnosis of lead toxicosis following ingestion of fishing tackle. Waterfowl examined at our laboratory that had died of lead toxicosis all had gizzards full of lead shot. The number of cases of lead intoxication involving waterfowl remained pretty steady through 2009, when I retired. The US ban on lead shot for hunting waterfowl in 1991 seemingly had little effect on the steady number of cases we saw.

The effects of lead ammunition and fishing gear on animals are complex. Perhaps it is time for the AVMA to take a proactive position on the use of lead ammunition and fishing gear.

William P. Higgins, dvm, phd

Glen Elm Equine Veterinary Services Centreville, Md

Gary Block, dvm, ms

Ocean State Veterinary Specialists East Greenwich, RI

In 1991, the federal government instituted a nationwide ban on the use of lead shot for hunting waterfowl. Since then, 30 states have implemented additional restrictions beyond those 1991 federal waterfowl regulations. Clearly, there is substantial interest across the country in reducing the environmental impact of lead as a by-product of recreational activities. Nevertheless, lead ammunition continues to adversely affect many animals, including predators that hunt birds and other wildlife and scavengers that eat from carcasses and offal piles.¹ Humans, particularly children, who unknowingly consume tiny lead fragments in game meat can also be harmed.

California was the first state to enact legislation to gradually eliminate the use of lead ammunition for sport hunting statewide. The state requirement to use nonlead ammunition alternatives will begin in 2016 and will be fully implemented for the taking of all wildlife by 2019. In 2014, a bill was introduced in Rhode Island (H 7838/S 2628) that would have phased out the use of lead ammunition. Unfortunately, this bill did not move forward, but similar legislative efforts will undoubtedly continue to be made.

Opponents often portray such bills as anti-gun legislation. This is not the case. A statewide survey² conducted in April 2014 by Mason-Dixon Polling & Research revealed that Rhode Island voters support legislation to require the use of nonlead ammunition for the taking of wildlife, with 62% of Rhode Island voters favoring such a phaseout and only 28% opposing it.

The scientific evidence substantiating the toxicity of lead and its negative impacts on health and the environment is overwhelming. A change from lead ammunition to nonlead alternatives seems to me to be a small sacrifice when compared with the potential benefits to animal and human health. We cannot expect to reach unanimous agreement on this issue. Nevertheless, I believe the AVMA should take a leadership role within the veterinary profession, stepping forward and swiftly formulating a policy urging the elimination of lead from all ammunition and fishing tackle.

Writing on behalf of the Humane Society Veterinary Medical Association (HSVMA), I want to express the association's agreement with the authors of the recent commentary “Are there legitimate reasons to retain lead ammunition and fishing gear?”¹ and suggest that the answer to the question posed by their title is a decided no.

Ammunition is the largest unregulated source of lead knowingly discharged into the environment in this country. Inadvertent ingestion of lead ammunition and fishing tackle by birds and mammals—both predator and scavenger species—and of residual lead in the meat of game species by humans can contribute to suffering, illness, and death.

The HSVMA maintains that there is ample scientific evidence to support common-sense reform on this issue to protect animal, human, and environmental health. The CDC has concluded that “no safe blood lead level has been identified,”² and in 2013, a group of more than two dozen specialists in veterinary medicine, conservation medicine, environmental health, neurology, pediatrics, toxicology, public health, and wildlife epidemiology published the report Health Risks from Lead-Based Ammunition in the Environment—A Consensus Statement of Scientists³ calling for the reduction and eventual elimination of lead from ammunition.

The AVMA has described one health as “the integrative effort of multiple disciplines working locally, nationally, and globally to attain optimal health for people, animals, and the environment,” indicating that “the health of each is inextricably connected to the others,”⁴ and has encouraged veterinarians to “become more aware of and proactive with issues which impact the health of animals, humans, and the environment.”⁵ Given the well-documented risks associated with their use, the HSVMA believes that lead-based ammunition and fishing tackle are among those issues.

In 2013, Governor Jerry Brown signed Assembly Bill 711, which requires a complete ban on the use of lead ammunition for any hunting purposes by July 1, 2019, making California the first state to implement a statewide phaseout of the use of lead ammunition for the taking of wildlife.⁶ We believe that the time is right for veterinary professionals to join their human and environmental health colleagues in supporting the removal of lead from ammunition and fishing tackle, and we urge the AVMA to take an influential role in these efforts by adopting a clear policy encouraging the elimination of lead from hunting ammunition and fishing tackle nationwide.

Barbara Hodges, dvm, mba

Veterinary Advisor Humane Society Veterinary Medical Association Davis, Calif