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Cancer is among the most feared diseases by pet owner. For many owners, the diagnosis brings grief, uncertainty, fear, and a general feeling of hopelessness.

While it is true that cancers can result in the untimely death of our pets, not all cancers carry a poor prognosis. For example, many solid tumors, if diagnosed early, respond quite well to surgical removal before they have spread. In these instances, early surgery is curative.

Other cancers may not be diagnosed until they have already spread. In these instances, treatment may not cure the pet but instead will provide a comfortable, extended life. In this latter case, the goal is to prolong life, but also ensure the pet is comfortable and has a good quality of life in whatever time remains. For most pets, the diagnosis of cancer is not an immediate death sentence, but rather the chance to begin therapy. Few cancers truly spread quickly. By keeping up with regular veterinary examinations and laboratory tests, early diagnosis of cancer is possible in most dogs and cats.


There are actually several recognized causes of cancers in pets.

VIRUSES. In cats, the feline leukemia virus, feline sarcoma virus, and feline immunodeficiency virus directly or indirectly through suppression of the immune system cause cancer.

TOXINS. In dogs, exposure to certain chemicals including 2,4-D can cause cancer. Various food additives have also demonstrated carcinogenic activity in laboratory animals, prompting many owners to prepare food at home or select diets that do not contain these synthetic additives and preservatives.

VACCINATIONS. Doctors are now beginning to realize that in a very small percentage of cats, frequent immunizations may cause certain solid tumors to develop. This is a very controversial topic, and the exact reason why a very rare number of cats that receive vaccinations, or other injectable medications, develop cancer is not known. Current evidence suggests that in genetically susceptible pets, some component of the vaccine, or injection, may cause a local reaction that becomes cancer.

GENETICS. Some pets are genetically prone to cancers. For example, among dogs, the Boxer is well known to develop cancers at a much higher rate than other breeds. Large breed dogs such as Retrievers have a higher incidence of malignant tumors of the spleen and liver. These examples may be a result of the inheritability of certain types of cancers, similar to the situation that occurs with some types of cancers in people (retinoblastoma) that occur as a result of genetic defects.

AGING. Most cancers occur in older pets. The exact reason is not known, but it seems that these older pets may have decreased functioning of the immune system.

Normally, as cells divide, mutations arise. In most pets, these abnormal, mutated cells are killed by their immune systems. Cancers arise when the immune system fails to kill these mutated cells. This seems to occur at a higher frequency in older pets. On a cellular level, here is how cancer forms and spreads.

It is know that malignant cellular transformation is associated with a series of genetic changes occurring within the cell. Cells contain proto-oncogenes, normal sequences of DNA, which regulate cellular responses to external signals that stimulate cell growth and reproduction. Proto-oncogenes are called simply oncogenes if their level of expression is altered so that the cell gains the potential for malignant transformation. Oncogenes may be activated in an aberrant manner in several ways, including:

  • Point mutations can occur as a result of cell damage, altering the behavior of normal genes.
  • Amplification of oncogenes can occur, altering the processing of cellular signals.
  • Tumor suppressor genes, normally acting to restrict cell proliferation, can be diminished, allowing the formation and spread of cancer.

Once these cellular defects occur, mutated (cancerous) cells can reproduce and spread, causing what is called "cancer."

The main natural treatments are designed to boost the immune system and reduce the spread of cancer. These can be used in conjunction with conventional therapies, as they are unlikely to be effective by themselves in most patients. The natural treatments are widely used with variable success but have not been thoroughly investigated and proven.

While there are few controlled studies showing the value of diet in supporting the pet with every type of cancer, there are studies showing the benefits of dietary therapy when combined with conventional therapies in dogs with lymphoma and nasal tumors. Since this diet is designed to reduce the growth and spread of cancer, it is often recommended for dogs and cats with any type of cancerous disease.

Studies demonstrate that both people and pets with inadequate nutrition cannot metabolize chemotherapy drugs adequately, which predisposes them to toxicity and poor therapeutic response. This makes proper diet and nutritional supplementation an important part of cancer therapy. There are several metabolic derangements common in the cancer patient. First, cancer patients often have hyperlactatemia (increased lactic acid in the blood). Additionally, since metabolism of simple carbohydrates produces lactate, a diet with a minimum of these carbohydrates might be preferred.

Research has shown a pronounced decrease in certain amino acids such as arginine in the plasma of cancer patients. If left uncorrected, these amino acid deficiencies could result in serious health risks to the patient. Supplementation with the deficient amino acids might improve immune function and positively affect treatment and survival rates.

Weight loss often occurs in cancer patients as a result of cachexia (wasting). Most of the weight loss seen in cancer patients experiencing cancer cachexia occurs as a result of depleted body fat stores. Tumor cells, unlike normal healthy cells, have difficulty utilizing lipids for energy. Dogs with lymphoma fed diets high in fat had longer remission periods than dogs fed high carbohydrate diets.

While there are often many treatment options for the various malignancies experienced by our patients, we often overlook the simple aspect of nutrition. Prevention and treatment will in the future most likely focus on nutrition in veterinary medicine, just as our counterparts are now doing in the human medical field. The research is out there: There is no doubt that cancer patients have deranged nutrient metabolism that can negatively affect the outcome of conventional therapies. Additions of omega-3 fatty acids and antioxidant vitamins and minerals to the diet of cancer patients may help improve survival and possibly decrease the chances of pets contracting cancer in those who are currently cancer-free.

Next month we will talk about the different diets available for pets with cancer.

Shawn Messonnier, DVM

As my thank you for reading my articles, enter code “drshawn” at my natural products web store,, to save 10% on all your future purchases!

Shawn Messonnier DVM Past Supporting Member, Oncology Association of Naturopathic Physicians Author, the award-winning The Natural Health Bible for Dogs & Cats, The Natural Vet’s Guide to Preventing and Treating Cancer in Dogs, and Breast Choices for the Best Chances: Your Breasts, Your Life, and How YOU Can Win The Battle!

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