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Neoplasia in Dogs

Reviewed by Dr. Celeste Clements, DVM, DACVIM on Wednesday, July 1, 2015
Posted July 06, 2015 in Dog Diseases & Conditions A-Z

Boston Terrier looking into the cameraNeoplasia is the term for various types of abnormal growths. According to Dr. Ananya Mandal, of NewsMedical.net, neoplasms can be benign or malignant. The terms neoplasia, tumor and cancer are sometimes used interchangeably and may refer to various types of growths (even non-cancerous or benign growths).

How do neoplasms arise?
To understand how abnormal cells grow, you have to understand how normal cell growth is regulated. Throughout life, cells are continually being born and dying1. When that process is disrupted, cells behave abnormally and abnormal tissues form (neoplasms).

General types of neoplasia
There are two primary types of neoplasia:

  • Benign— Benign neoplasms do not invade normal tissue, do not spread to other parts of the body and are rarely fatal, unless they put pressure on a vital organ.
  • Malignant— Malignant neoplasms (commonly referred to as cancer) invade and destroy tissue around them. They grow faster than the tissue around them and bits of the tumor, called metastases, can break off and spread to other parts of the body forming other tumors.

Where could neoplasms occur?
Neoplasms could appear in:

  • The Skin— Skin neoplasms are common in dogs
  • The Breast (Mammary Gland)— Half of all breast neoplasms in dogs are malignant
  • The Head & Neck— Neoplasia of the mouth may result in a mass or tumor on the gums, bleeding, odor or difficulty eating
  • The Testicles— Testicular neoplasia is common in dogs particularly with retained (undescended) testicles
  • The Abdomen— Neoplasms inside the abdomen are common. Weight loss or abdominal swelling can be signs of abdominal neoplasia
  • The Bones— Bone neoplasms are common in large and “giant” breeds of dogs. The leg bones, near joints, are the most common sites
  • The Lungs— Lung tumors are uncommon, but possible, in dogs
  • The Urinary tract— Tumors of the reproductive and urinary tract are not uncommon. Neoplasia can arise from the prostate, urinary bladder and even the kidneys.
  • The immune system— Lymphoma is a common form of neoplasia in dogs

Neoplasia and the kidneys
In dogs, neoplasms of the kidneys are uncommon, but dangerous; metastatic tumors are more common2,3. Renal carcinoma is the most common renal tumor in dogs and may occur bilaterally.

What are the symptoms of neoplasia in dogs?
Symptoms include:

  • Abnormal swellings that persist or continue to grow
  • Sores that do not heal
  • Weight loss
  • Loss of appetite
  • Bleeding or discharge from any bodily opening
  • Offensive odor
  • Difficulty eating or swallowing
  • Hesitation to exercise or loss of stamina
  • Persistent lameness or stiffness
  • Difficulty breathing, urinating or defecating  

Most forms of malignant neoplasia will ultimately result in weight loss, listlessness and reluctance to eat. Specific signs of cancer may vary, depending on what part of the body is involved. For instance, gastrointestinal cancers often result in vomiting and diarrhea, while tumors of the nervous system may result in seizures.
Early detection of cancer is always important to improve the odds of success if treatment is elected.

How much of a risk are neoplasms to your dog?
It has been pointed out that some breeds of dogs are more prone to develop neoplasms than others. As is often the case in human medicine, the cause of cancer in any individual dog is often unknown and may include genetic predispositions or exposure to a number of things that induce changes in cells. Older dogs are more at risk for neoplasia than young dogs.

Is neoplasia becoming more common?
Neoplasia is already common in pet animals and the incidence increases with age. Cancer accounts for almost half of the deaths of pets over 10 years of age4.

In general, cancers affect older dogs more commonly than younger dogs. In many cases, cancers will grow over quite a long period of time. Because some dogs are living far longer than they used to and veterinarians are much more aware of the potential for neoplasia, we are probably at least seeing and diagnosing more dogs with neoplastic diseases.

How are neoplasms diagnosed?
In addition to a thorough physical examination, your veterinarian will likely recommend blood and urine tests, and imaging studies such as radiographs, ultrasound, CT or MRI studies to define the extent of the cancer. If there is a suspicion of neoplasia, your veterinarian will recommend a biopsy to confirm the diagnosis and the source of the neoplasm.

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Mike has more than 35 years of experience in companion animal veterinary practice and is a valued member of IDEXX’s Pet Health Network team since 2013.