General symptoms of cancer
Cancer is a word that triggers powerful emotions. We often hear people say that someone "has cancer" or that research is focused on "fighting cancer". In fact, cancer is not one single disease, and it would be more accurate to refer to the different types of cancer and the organs they affect.
Advances in health care and nutrition have considerably increased our pets' life expectancy. As our pets age, however, the normal process of cell division is increasingly likely to become deregulated, and the body's natural protective mechanisms can fail. Cancers reportedly account for the death of some 45% of dogs over the age of 10. This is a significant figure and merits closer examination.
In some cases, a specific cancer is easy to diagnose, because its symptoms are readily visible (e.g. a subcutaneous mass). In other cases, cancers are harder to spot, because their manifestations are subtle and their systemic symptoms can be non-specific. Just as in humans, several diseases can present similarly. It takes experience, a meticulous physical examination and diagnostic tests to identify the true cause of the health problem.
Cancer sometimes reveals itself through paraneoplastic syndromes (PNS). These systemic manifestations of changes or disruptions caused by tumours can be the first symptoms of cancer, and some of them are characteristic of certain tumours. However, paraneoplastic syndromes are not necessarily associated with cancer, which is why the presence of one or more symptoms of PNS requires a thorough examination and a number of diagnostic tests.
Cachexia, dysorexia and anorexia
Cachexia is the loss of lean body mass (muscle) that occurs even though the animal's appetite is not impaired and it is eating food of adequate quality and in sufficient quantity. Dysorexia is diminished appetite and anorexia is a complete loss of appetite; both conditions lead to inadequate nutrient intake. The metabolic changes associated with these conditions sometimes appear before any weight loss is noticed. Weight loss can be so gradual that it is difficult for owners to spot, especially as their pet's coat can conceal its body condition. Additionally, loss of lean body mass can occur without a loss of fat mass and in spite of persistent overweight. An annual physical examination can help detect these symptoms and identify their cause.
In dogs, the most common causes of hypercalcemia (above normal levels of calcium in the blood) are cancers such as lymphoma, anal gland tumours and carcinomas. Elevated blood calcium levels can have adverse effects. For example, the first clinical manifestation of hypercalcemia is usually impaired kidney function, which can present as weakness, increased thirst, abundant urination, anorexia and vomiting. Since these symptoms may be due to several diseases, your veterinarian will suggest blood tests. The test results will help him explain what is going on in your pet's body.
Abnormally low blood glucose levels can arise from a variety of conditions. Hypoglycemic animals are often weak, may lose consciousness or suffer convulsions. These problems do not necessarily point to cancer. In older dogs, however, the most common cause of hypoglycemia is the presence of an insulinoma, a tumour originating in the pancreas. As the name suggests, insulinomas secrete insulin and can cause a marked decrease in blood glucose levels.
Fever is a common symptom of many diseases. When an animal has a fever, the first cause that springs to mind is a viral or bacterial infection. In such cases, fever is a defense mechanism: the body increases its temperature sufficiently to kill off the infectious agent. Although infection is the primary cause of fever, it can also be caused by autoimmune diseases and cancers. This may be due to the invasion of normal body tissues, which usually triggers an immune response, or to the fact that cancer cells release inflammatory substances (such as cytokines and prostaglandins) into the blood.
Several other paraneoplastic symptoms can denote the presence of cancer. As the animal's owner, you are ideally placed to notice when your pet is off colour. If you notice that something is wrong, it is best to consult your veterinarian immediately rather than allowing the problem to worsen. After performing a complete physical examination, your veterinarian will draw on his expertise to recommend tests to determine what ails your pet and prescribe appropriate treatments. Rest assured that your pet will be in good hands. Its comfort and well-being are our highest priorities.