Tumour behaviour in Dogs
Prevalence of cancer, which means number of diagnosed cancer cases per year, is increasing through years for a variety of reasons, but mostly because of animals living to increasingly older ages and the availability of better health care treatments. Cancer diseases stay the major cause of pet animal death. One of the big difficulties with animal cancer is that the pet cannot tell when he feels something wrong is happening, thus the owners need to bring every change to the attention of their veterinarian. Recognition of tumour related symptoms can facilitate early tumour diagnosis and treatment.
Definition of a tumour
A tumour is an abnormal growth of cells on or within the body and may be benign (slow growing, without spreading throughout the body) or malignant (aggressive, with a tendency to metastasise). Cancer can affect any area of the body or any body system. A cellular diagnosis based on a biopsy or a fine needle aspiration of the tumoral cells is required to determine the type of cancer. Each tumour type within a location has a different behaviour, treatment and prognosis.
Clinical signs directly due to cancer
The warning signs of cancer in dogs are very similar to that in people, because they share the same types of tumour. Some common type of cancer in dogs include skin tumour, mammary gland tumour, testicular tumour, bone tumour, lymphoma… In many instances malignant tumours arising in the organs of the body will cause symptoms directly related to the location of the tumour.
Such symptoms are alarming when they become chronic and may include:
- Lump that has been arising or changing in size or consistency. Benign skin tumour such as fatty tumours or warts are the most common lump encountered. To distinguish between these harmless lumps and more aggressive ones, aspect of the lump might be helpful. In fact malignant tumours are often fast-growing, hard, painful, hairless and/or ulcerated.
- Changing in bowel habits, mostly vomiting, diarrhea or difficulty defecating. Those symptoms might be warning signs of a tumour of the digestive tract. Bloody stool may also be encountered: the blood may or may not be bright red. In fact blood can be digested in the first portions of the intestines and get the appearance of coffee grounds by the time the dog poops it out.
- Eurologic syndrome such as disorientation, abnormal behavior, seizures, paralysis, may be caused by a tumour of the spinal cord or the brain.
- Enlarged lymph nodes can be consistent with reactive inflammation or infection but may also be the warning sign of a lymphoma. Most of the time enlarged lymph node associated with lymphoma are hard and arise in many parts of the body.
- Difficulties urinating, increased frequency or urgency of urination, or even bloody urine might be expression of a cystitis but also of a tumour of the bladder. Most bladder tumours arise from the back part of the bladder and can cause a partial or complete obstruction of the urinary tract.
- Difficulties in breathing may be due to development of a tumour taking up space normally devoted to lung expansion. Any tumour of the chest cavity or close to the diaphragm can cause breathing difficulties. Those are consistent with breathing unusually fast, labored or noisy breathing, breathing with an open mouth, coughing.
- Difficulties in eating or swallowing might be due to oral cavity tumour. In dogs numerous benign growths can happen in the mouth, they have usually well defined boarders and don’t invade the adjacent bone or spread throughout the body. More aggressive tumour such as melanoma or fibrosarcoma are locally invasive and can metastasize.
- Those are classic signs but sometimes there are little or no signs, at least early on. Additionnal warning signs such as persistent lameness or stiffness related to bone tumours, a sore that doesn’t heal related to skin tumour, or more generally unexplained chronic discharge from any body opening may be noticed.
Canine paraneoplastic syndrome
Paraneoplastic syndrome is a symptom or a group of symptoms that are non-specific and consequence of the presence of a tumour in the body. Those disorders are indirect and are usually caused by tumour cell secretions, that is to say small molecules released in the circulation. Thus they may be seen at sites distant from the location of the tumour.
The paraneoplastic syndrome parallels the underlying tumour, and, therefore, successful treatment of the cancer leads to disappearance of those symptoms. Sometimes the symptoms of this syndrome show before the diagnosis of the tumour, and the recognition of them might be helpful for an early tumour diagnosis. Such disorders include loss of appetite, lethargy, weight loss/ poor body condition, fever, increased water intake (more than 100 mL/kg/day) and urination.
Some endocrinologic manifestations may also be related to cancer. For example, hypercalcaemia, which clinical manifestations are vomiting and increased water intake, is commonly related to lymphoma or anal tumour. Hypoglycaemia might also be associated to cancer, mostly secondary to a pancreatic tumour. Its clinical expression include weakness, disorientation and seizures.
It is important to keep in mind that those symptoms are completely non-specific and may be due to another cause than cancer. Early diagnosis and treatment are key to a favourable prognosis, whatever the cause of the symptoms.