According to the National Canine Cancer Foundation (NCCF), one out of every three dogs will be diagnosed with cancer. But what exactly constitutes a cancer? Contrary to popular opinion, not every ugly mass, growth, or tumor qualifies.
Cancer is perhaps best defined as a disease caused by the uncontrolled division of abnormal cells. A cancer originates in one single tissue of the body but may sometimes affect faraway organs as it spreads, typically through the circulatory and lymphatic systems.
As in humans, cancers are often strongly linked to genetic factors, which makes them more prevalent in certain breeds and within specific genetic lines within those breeds. Which means that some cancers are more common in dogs than they are in humans. Here’s a list of the more common cancers, by body system:
Lymphoma: This blood cancer is way too prevalent in dogs. It often runs in genetic lines and is, consequently, more prevalent in certain breeds. Golden Retrievers are the poster children for this disease, but any breed can get it. Though it’s considered a blood cancer, this cancer can set up residence as a tumor in many organs, including the spleen, intestines, kidneys, and even the skin.
Hemangiosarcoma: This tumor type is commonest in the spleen, but anywhere blood goes is a potential location (aka, most anywhere).
The liver is a site where lots of blood flows. Consequently, it’s exposed to a barrage of cells from other parts of the body. If they happen to be cancerous cells, they may take up residence here. These types of tumors are termed metastatic (or secondary) cancers.
Primary liver tumors (those that originate in the liver) are most typically bile duct adenocarcinomas, but plenty of tumors (from the GI system and spleen, for example) like to metastasize here, setting up secondary residence.
Mast cell tumors: Mast cell tumors are the most common cancers of the skin. These tumors differ widely in their level of malignancy, so while some are easily treated by simple removal (and careful observation of the site for recurrence down the road), others require chemotherapy and even radiation therapy. That’s one reason why the laboratory testing of tumors is essential!
Lipoma/liposarcoma: Lipomas, arising from the fatty tissue on the skin, are the most common benign tumor in dogs. However, the rare lipoma might not be what it seems. If these common skin bumps start to change (apart from growth, which most of them do to some extent), it’s time to take them off and test them! The malignant version of this tumor is called a liposarcoma.
Perianal adenoma/adenosarcoma: Originating in the tiny skin glands around the anus, this tumor is typically benign (adenoma), but the malignant version is possible too (adenosarcoma), particularly those that arise from the anal gland tissue itself.
Hemangiosarcoma: These tumors can emerge from the blood vessels in the skin, as well as the vessels in the internal organs as stated in the above blood section. In the skin, this typically looks like blood blisters and tend to have irregular margins. A benign version of this tumor is called a hemangioma. UV light exposure has been linked to both these kinds of growths.
Soft tissue sarcoma: These are more common in cats, but they can happen in dogs too. They arise from the fibrous connective tissues in the skin and can be very aggressive. Rapid removal is essential!
Squamous cell carcinoma: While these tumors don’t tend to spread, they are usually very locally aggressive, destroying bone and other connective tissue along their path. They’re typically red and bleeding by the time it’s identified. They can also occur elsewhere, like in the penis and vulva of dogs.
Oral melanoma: As in humans, these can occur in the skin, but they’re not as prevalent here as they are in the oral cavity of both dogs and cats. The eyes and toes are other popular sites. Unfortunately, these tend to spread through the local lymph nodes and into the lungs.
Bones (and connective tissues)
Osteosarcoma: These are the most common tumors of the bone. They are more prevalent in larger breed dogs from certain genetic lines. There’s some evidence that they’re more common in sterilized dogs, but that’s still being hotly debated. These tumors are very painful and tend to metastasize to the lungs.
Chondrosarcoma: These are less common but tend to affect the cartilage. When they happen, they’re usually very aggressive.
Multiple myeloma: This tumor most typically affects the spine in dogs, lending a “moth-eaten” appearance to the vertebrae when X-rayed.
Adenocarcinoma: This malignancy can arise from any of the tissues of the GI system, but the stomach and intestines are predisposed.
Leiomeiosarcoma: A mouthful to say, and aggressive too, these tumors arise from the smooth muscles that line the GI tract.
Pancreatic tumors: Some of these are not strictly cancerous, but since the pancreas is such a sensitive and powerful creature, the results of any kind of tumor here can be devastating to the whole body. Insulinomas, adenomas, and others can be deadly.
Primary lung tumors: Though most tumors of the lungs in dogs spread here from elsewhere (called metastatic tumors), some can originate here too. Adenocarcinoma and alveolar carcinoma are the main two types among these.
Mammary carcinoma or adenocarcinoma: These are the most common kind of cancers of the mammary glands. They do not occur in dogs spayed before puberty (six months of age) and are considered uncommon in dogs spayed before 2 or 3 years of age.
Leiomeiosarcoma: Though rare, these tumors of the uterus can be aggressive.
Prostatic adenocarcinoma: These are really uncommon. Surprisingly, when they do happen, they tend to do so in neutered dogs.
Transitional cell carcinoma: This tumor originates in the wall of the bladder and tends to be very irritating. Blood in the urine is the most common sign.
Adrenal (adrenocortical) adenoma/adenocarcinoma: While benign tumors (adenomas) are most common here, the malignant version (adenocarcinoma) can happen too.
Thyroid adenocarcinoma: This one is locally aggressive and can cause trouble swallowing and breathing. Any lump under the neck should be addressed ASAP!
Pituitary adenoma: Strictly speaking, these are benign and usually so small as to be microscopic. Which is a good thing seeing as the pituitary gland is in the brain! However, they typically lead to Cushing’s Disease, which is a serious disease of the adrenal glands.
This is by no means an exhaustive list, but it comprises the basic kinds of cancers.
As always, see your veterinarian if you think your dog might have cancer. The most common signs include weight loss, a diminished appetite, vomiting, a visible mass, and trouble breathing. Any “off” or unusual behavior is always a reason to see your veterinarian.