thoughtful dog

Dr. Sue Cancer Vet Interview from 2012

This article, from the site AngryVet,  is dated December 2012, but the topics discussed continue to be relevant.

I recently came across this interview between Dr. Rob and Dr. Sue Ettinger and thought the information Dr. Sue provides, especially on spaying, neutering, and the incidence of cancer, very valuable. Additionally, the idea of a cancer registry for tracking cancers in dogs and cats (as is done for people), is an important idea that several groups are now beginning to address.

 

Dr. Rob: One of the things that gives me pleasure  is that Angryvet gives me the opportunity to provide the public direct access to some of the brightest and most progressive veterinarians and scientists in the field of veterinary medicine today.   What really freaks me out (I guess I am getting old) is that some of these pioneers are former classmates of mine.  This week it is my pleasure to introduce to you Dr. Susan Ettinger.  Dr. Ettinger was a classmate and friend of mine at Cornell University.  Today she is a Board Certified Veterinary Oncologist.  She has been featured on talk radio, practices at a specialty facility in Yonkers, NY, and is the co-author of the book The Dog Cancer Survival Guide.  I encourage you to visit her website,   and to “like” her Facebook page.

The interview consisted of questions that were intended to be thought provoking, relative, and at times controversial (I hope at this point you wouldn’t expect anything else).  Dr. Sue was kind enough to provide detailed and well-researched  answers to my questions.

Q.   There are a number of cancers that are rising in humans (breast cancer, various children’s cancers, rectal cancer etc.). There are many theories as to why this is happening (environmental toxins, diet, increased awareness and detection, etc.). The question is:  Do we track cancer rates in animals and are there any cancer rates that are on the rise in our pets? If so, to what do you attribute these increases?

A.  Unfortunately we do not track cancers in dogs and cats, like we do in people. When dog cancer incidence is reported, it is often based on comprehensive registry done from 1963-1966 in 2 northern Californian counties. Before I started my medical oncology residency, I assisted Dr. Rod Page at CU CVM with the logistics to starting a New York State Registry.

A cancer registry maps where cancer patients live and where various types of cancer occur. For example, The New York State Department of Health has a human cancer registry in place, and we wanted to start a registry to map cancer incidence data for dogs and cats.

Not only would it be helpful to know if cancer rates are on the rise; knowing the cancer rates in pets is a valuable predictor for cancer risk assessment in humans. Dogs and cats live alongside their human companions. While they share some risk factors for cancer with us, including exposure to second-hand smoke, environmental chemicals, and inherited risk factors, they don’t drink alcohol, smoke or make other lifestyle choices. Companion animals generally develop cancer due to environmental or inherited factors or a combination of the two.

First we need to know the total number of dogs or cats at risk, the denominator. Unfortunately this is not known since we don’t have a census like for people. Although most cities and towns require dogs to be registered, records are far from complete. Cats are not tracked either. The second number we need is the number of diagnosed cancers, the numerator. Cancer is not a reportable disease in pets, so it is not tracked. In addition, many cases are not diagnosed, just suspected.

The Veterinary Medical Database collect patient data from 26 university teaching hospitals in the US and Canada, and this data is widely used as cancer surveillance information. Since the info is based on referral hospital cases, it is not representation of the general population. If you don’t go to a referral center, the cancer is not getting reported.

In 2008, a study was published in JVIM (Merlo, 2008) out of Genoa Italy, summarizing cancer incidence from 1985 to 2002 with The Animal Tumor Registry (ATR). 6743 tumor biopsy specimens were received from local veterinarians, and 3303 (48.9%) biopsy specimen samples were diagnosed as cancer. Mammary cancer was the most frequently diagnosed cancer in female dogs, accounting for 70% of all cancer cases. The highest incidence rates were detected for mammary cancer and for non-Hodgkin’s lymphoma in intact female dogs and for non-Hodgkin’s lymphoma and skin cancer in male dogs. All cancer incidence rates increased with age. All cancer incidence was 3 times higher in female than in male dogs, a difference explained by the high rate of mammary cancer observed in intact female dogs. Because a biopsy specimen was required to make a cancer diagnosis, cancer rates for internal organs cancers, such as respiratory and digestive tract cancers may have been underestimated in the study population.

While these registries are useful, there are unfortunately limited registries available for dogs and cats.

Q. Many have traditionally argued that spaying female dogs and cats (early before the first heat) is crucial for preventing mammary cancer and of course uterine and ovarian cancers (extremely rare of course). A similar argument is made in male animals for preventing testicular cancers. What they do not point out to is that other cancer rates are actually DECREASED in intact animals (hemangiosarcoma, osteosarcoma, and even prostatic cancer etc.). As you know, we at angryvet.com feel that the issue of early spaying and neutering is controversial at best; and since there are at least there are two sides to the argument, an owner needs to weigh all of the options when making the decision to “fix” (are they broken?) an animal. What are the facts, with statistics if they are available, on spaying and neutering with regard to cancer prevention?  And what are your thoughts on spaying and neutering, in particular spaying and neutering before puberty.

A. Hormones may promote or inhibit cancers, depending on the sex of the dog and the tissue or organ. For breast cancers in dogs, less exposure to female sex hormones has been shown to be protective, which is important since mammary cancer is the second most common form of dog cancer. Breast cancers can be nearly completely eliminated by spaying a female dog before the first heat. On average, the first heat arrives at six months of age and recurs approximately every six months until late in life.

Spaying provides less protection for canine breast cancer with every passing heat. Studies have shown that dogs spayed before the first heat have a 0.05% risk of developing mammary cancer, when compared to intact female dogs, which means the risk is almost completely eliminated by the surgery. If the spay happens between the first and second heats, female dogs still have quite a bit of protection, with only an 8% risk, compared to their intact sisters. If the spay happens between the third and fourth heat, female dogs have a 26% risk, compared to intact dogs. Clearly, spaying a female dog reduces her risk of mammary cancer. It also removes all risk for ovarian and uterine cancer.

For a male dog, neutering decreases the risk of benign perianal adenomas (which are stimulated by testosterone) and also eliminates his risk for testicular cancer. If you just look at these factors, spaying and neutering might seem like an obvious choice.
But more recently, there is evidence that less exposure to sex hormones increases risk for other aggressive cancers, including osteosarcoma, bladder transitional cell carcinoma, and prostate cancer.

Purebred dogs who have been spayed or neutered are twice as likely to develop osteosarcoma (bone cancer), and the risk is even higher for Rottweilers. One study showed that both male and female Rotties, who were surgically sterilized before the age of one year, had an approximately one in four risk for developing osteosarcoma during their lifetime, while intact Rotties were much less likely to develop the disease.

Spaying has also been shown to increase the risk of lymphoma, and other studies show that castration increases the risk for developing transitional cell carcinoma (bladder cancer) by three to four times. Spaying and neutering also increases the risk of prostate cancers and hemangiosarcoma of the heart.

Osteosarcoma, transitional cell carcinoma, hemangiosarcoma of the heart and lymphoma are generally more aggressive than mammary cancer – 75% of mammary cancers are cured with surgery alone.

These factors should be considered when we decide whether to spay and neuter our dogs. In the US, there is widespread recommendation for early spaying and neutering. In addition to the benefits above, spay/neuter also helps to reduce uterine infections (pyometras), and, in some cases, unwanted behaviors like humping, marking, and aggression. How will we reconcile population control and the euthanasia of unwanted pets with the associations between spaying, neutering, and cancer development?

Because the increased cancer risks from spaying and neutering are serious, pet guardians should consider the big picture when evaluating the timing of these procedures. This topic is also discussed in my book, the Dog Cancer Survival Guide. Here, our recommendation is:

– to spay females sometime between the third and fourth heats – which will have the added benefit of reducing the risk of mammary cancer;

– to neuter males sometime between the ages of eighteen and twenty-four months.

Most dogs reach sexual maturity at about twenty-four months, approximately at the fourth heat in females. At this point in their development, dogs have received the protective benefit of adult sexual hormones and are at a decreased risk for the cancers mentioned above. This recommendation is not one size fits all. Consider your breed’s risk for cancers. I recommend you consult with your vet to make a decision on a case-by-case basis.

Q: Many of the goals of an oncologist are to treat (surgery, radiation, chemotherapy etc.) cancer.  Is there any research being done with regards to cancer prevention?  Has diet been looked at?  Has supplementation been looked into (for example Vitamin D research in people was a previous Angryvet blog)?

A: You are correct. The majority of my training as a boarded medical oncologist has focused on the how cells become cancers at the molecular level, the behavior, diagnosis and prognosis of the cancers themselves, and treatment (mostly chemotherapy, surgery, and radiation). Diet, supplementation, and prevention are relatively newer areas of research, and there is much work to be done.

On the research of prevention, there are studies designed to identify risk factors and to assess new approaches to reduce the risk of developing certain types of cancer. Such studies typically involve lifestyle, such as diets and supplements, and the examination of risk factors. This type of study, or clinical trial, is called a prevention trial.

In people, the two major nutritional factors directly associated with risk of developing cancer are obesity and low fruit and vegetable consumption. Low fruit and vegetable consumption has been linked to lymphoma, leukemia, breast, colon, and prostate cancer.

In dogs and cats, there are a few studies looking at lifestyle and cancer.  I talked about the effect of spay/neuter status in Rottweilers with osteosarcoma (bone cancer), in my previous AngeyVet post. Purebred dogs that had been spayed or neutered are twice as likely to develop osteosarcoma and the risk is even higher for Rottweilers. One study showed that both male and female Rotties, who were surgically sterilized before the age of one year, had an approximately one in four risk for developing osteosarcoma during their lifetime, while intact Rotties were much less likely to develop the disease (Cooley DM et al.  Endogenous gonadal hormone exposure and bone sarcoma risk. Cancer Epidemiol Biomarkers Prev. 2002 Nov;11(11):1434-40.).

Early obesity seems to play a role in mammary (breast) cancer in dogs. Dogs with lean bodies from 9-12 months of age were at decreased risk, while overweight dogs were at increased risk. In this study a high fat diet was not a risk factor, nor was obesity at time of tumor diagnosis. (Sonnenschein EG et al. Body conformation, diet, and risk of breast cancer in pet dogs: a case-control stud (Sonnenschein EG et al. Body conformation, diet, and risk of breast cancer in pet dogs: a case-control study.  Am J Epidemiol. 1991 Apr 1;133(7):694-703.).

In another study, females on homemade diet were at higher risk, as were dogs that ate a lot of red meat, especially beef and pork, and little chicken. This study also found older age, obesity at 1 year of age and 1 year before the diagnosis of mammary nodules to be significantly related to a higher prevalence of mammary tumors and dysplasias (Pérez Alenza D et al. Relation between habitual diet and canine mammary tumors in a case-control study.  J Vet Intern Med. 1998 May-Jun;12(3):132-9.).

Dietary fats also contribute to mammary cancer. A low-fat, high-protein diet has been associated with longer survival times (ST) for dogs with breast cancer, than a low-fat, low-protein diet. But in this study, high-fat diet did NOT affect disease, regardless of protein intake.

I know it’s confusing! Reading this, you may think a homemade diet is not a good idea. This is not my point at all. Many “homemade diets” are poorly balanced, have different protein sources, and made up of table scraps. This is hardly the same as a well-balanced and complete homemade diet. This is a complex topic, and these studies don’t often account for ingredient quality, digestibility, and other important factors like veterinary care. (If your dog does have mammary cancer, I would consider using chicken and lean meats for the protein, and skipping beef and pork.)

Another interesting study has looked at Scottish Terriers. This breed is predisposed to bladder transitional cell carcinoma (TCC). The addition of veggies at least three times a week along with their normal diet decreased the cancer incidence. Carrots given as treated were given most frequently in the study. This study also showed that the TCC risk was higher in Scotties that had been exposed to lawn herbicides, or herbicide and insecticides, than in dogs not exposed.

This study leads to some good recommendations: limit exposure to lawn chemicals and older flea products (topical fleas and dips), and feed veggies at least 3 times a week, especially in high risk TCC breeds. In addition to Scotties, high risk breeds include Shetland Sheepdogs, Beagles, Collies, and many terriers (Scotties, Westies, Airedales, and Wirehaired Fox). … TCC risk is also higher in neutered dogs – male and female – which goes back to my previous blog on the possible preventative benefit of sex hormones in some cancers.

As for vitamin D, this is one of the vitamins receiving attention with its role in cancer development in people and now pets.  Various cancers have been associated with low serum vitamin D concentrations, as it can promote tumorigenesis (tumor formation). In dogs and cats, unlike people, vitamin D status is dependent on dietary intake, and one would expect pets on commercial, balanced diets would have pretty stable levels.

An interesting recent study found Labrador retrievers with skin mast cell tumors (MCT) had lower serum vitamin D levels than Labs without MCT. We still do not know whether this is due to diet intake or a something related to the biology of dogs with MCT, but these findings suggest that low levels of serum vitamin D might be a risk factor for MCT in Labrador retrievers.

If low levels of vitamin D lead to MCT, can treatment cause tumor regression? Active vitamin D (calcitriol) is anti-proliferative to tumors at high doses, but high doses can lead to negative effects on patients like kidney damage, weakness, and calcification of soft tissues. In a recent study of dogs with MCT receiving calcitriol, there were adverse effects including hypercalcemia (high blood calcium), poor appetite and vomiting.

Can vitamin D supplementation help prevent MCT? What other cancers does vitamin D play a role, if any, in pets? There is much to be learned about cancer risk factors and prevention!

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