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How Fast Does Cancer Spread in Dogs?

Cancer in Dogs

Owners of dogs with cancer may be wondering how fast does cancer spread in dogs so to better understand what to expect. When it comes to cancer in dogs, there really aren't any exact timelines to refer to. Cancer is often unpredictable and several factors need to be kept into consideration. By looking at some studies involving dogs suffering from specific types of cancer along with a vet's experience in dealing with dog cancer, it is possible to attain some pointers on how fast cancer may spread in dogs but these are generally rough estimates.

Picture of cancer cells

Picture of cancer cells

Biology of Dog Cancer

In order to better understand how fast cancer spreads in dogs, it helps to comprehend how cells normally communicate. After grasping this concept, one can get a better understanding on the complexity involving the spread of cancer in dogs.

In a normal, healthy dog, cells are programmed to undergo several events. The cells start out as immature cells, then they mature, multiply and finally reach their main purpose. All cells have a specific purpose during their lifespan.

Cells that are damaged are also repaired and those that are no longer needed are replaced. This natural process is known as "apoptosis."

Cancer cells, on the other hand, do not follow the cycle that nature has programmed. While normal cells stop reproducing when there are enough cells, cancer cells do not. For example, let's imagine a cut on a dog's paw. Cells are produced to repair the cut in the skin, but the production will come to a halt once there are enough cells to fill the gap in the skin. Cancer cells instead will keep growing and may eventually form a cluster of cancer cells (tumor). Cancer cells also do not go through the process of being repaired or dying when they are damaged or old (apoptosis).

Did you know? Disease and cancer is suspected to occur when the process of apoptosis malfunctions and cells do not die as they should. Some supplements for dogs with cancer like Dr. Dressler's Apocaps can help induce apoptosis in cancer cells.


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How Dog Cancer Spreads 

Whether a cancer stays "local" or spreads to other body parts (a process known as metastasis), depends on the type of cancer and its stage.

Worth mentioning is another differential between normal cells and cancer cells: the ability to stick together. Normal cells produce substances that allow them to "stick" together in a group. Cancer cells on the other hand, lack the adhesion molecules which allows them to stick, and therefore, they have a tendency to float away to nearby areas or even travel through the bloodstream to distant regions of the body (metastasis).

Once the cancer cells arrive to the new region, they establish and start growing, forming tumors at the new location site, and surviving even if the original tumor is removed.

A good example of this is bone cancer in dogs (osteosarcoma). The cancer cells start eating the bone and spread to the dog's lungs forming nodules. Even if the dog's cancer-stricken leg is amputated, the cancer cells in the lung continue to grow.

Cancer can be compared to a copy machine. A good copy machine makes copies that are identical to each other. A copy machine that is malfunctioning may make a blotch on a copy and keep replicating copies with blotches on them. This blotch is a mutation that keeps on spreading out of control.

How Fast Cancer Spreads in Dogs 

The tissue sample taken from the liver is checked under a microscope.

A pathologist looks at biopsied tissue under a microscope.

Cancer cells tend to reproduce rapidly even before they are fully mature. This means they never get to mature into the specialized cells as normal cells do. Based on the level of maturation of cancer cells, it is possible to obtain the grade of a cancer.

Cancers are graded on a scale that may go from one to four, with one being the least aggressive and four being the most aggressive. This can be visible by looking at the cancer cells under a microscope. The grade of cancer in important when determining how fast a cancer is spreading in dogs.

For example, if the cancer cells closely resemble normal cells, then these are considered "well-differentiated" which means that they spread at a slower rate compared to cancer cells that are poorly differentiated.

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As mentioned, how fast a dog's cancer spreads depends on several factors such as the grade of the cancer and the type of cancer. Following are some general time frames as to how fast certain dog cancers spread.


How Fast Does Dog Bone Cancer Spread?

Bone cancer in dogs is a type of cancer that quickly spreads to the dog's lungs. "Osteosarcoma is highly metastatic and 90% of affected dogs are assumed to have metastatic disease at the time of diagnosis" points out Dr. Kim A. Selting, a veterinarian specializing in oncology.

In most cases though , no signs of cancer are seen on x-rays of the lungs because the newly formed tumors are too minuscule to be detected (micrometastasis). If there are signs of detectable spread to the lungs that are visible on x-ray (they appear as nodules), things are far more advanced and chemotherapy is not recommended, explains Dr. Laura D. Garrett, a veterinarian specializing in oncology.

Generally, without any treatment, survival times for dog bone cancer are quite short, just around 4 to 5 months, while dogs undergoing amputation along with chemo have survival times of about 1 year.

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How Fast Does Dog Spleen Cancer Spread?

dog gallbladder removal surgery

Spleen cancer (hemangiosarcoma) is also a cancer that quickly spreads. In this case, the cancer has a tendency to spread quite fast to the dog's liver (or even heart or lungs). When there is spread to the liver, removal of the spleen (splenectomy) might not be worthwhile, explains veterinarian Dr. Lee. 

With spleen cancer, survival rates once the tumor has spread are not very promising. A dog is lucky to get 3 to 6 months, points out veterinarian Dr. Andrea Robert. In some cases, it can even be less, even just one single month. The secondary cancers in the liver can start to bleed within a very short time. With this type of cancer, bleeding is a main issue.

Extensive bleeding from the liver or spleen can cause shock to rapidly set in. If surgery is not pursued, dogs need to be prevented from bumping the abdomen as it can happen when jumping off the couch or tripping down the stairs.

A secondary cancer to the liver can be ruled out or confirmed through an x-ray and ultrasound done before surgery.

"If it is one of the more nasty cancerous tumors (hemangiosarcoma) it usually will spread to other organs very quickly... If no spread is obviousthen I'd recommend surgery. There is always a chance that the ultrasound will be normal and your vet will still find spread in surgery (ultrasounds aren't perfect.)"~Dr. Dan, veterinarian.

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How Fast Does Oral Cancer Spread in Dogs? 

Oral melanomas are a type of cancer affecting dogs that are very likely to metastasize (spread to other body parts). A dog's local lymph noses may be involved and the cancer may spread to vital organs such as the dog's lungs. Spread to the lungs can be seen by x-ray or CT scan (more reliable) and such spread is seen as a late sign of oral melanoma.

How fast oral cancer in dogs spreads depends on the stage of the melanoma. Dogs with stage 1 oral melanomas measuring less than 2 cm and that has not spread, tend to have a medial survival time of 17 to 18 months following surgical removal of the mass.

Dogs with stage 2 oral melanoma measuring between 2 and 4 cm that has not spread, tend to have a median survival time of 5 to 6 months following surgical removal of the mass.

Dogs with stage 3 oral melanoma that is larger than 4 cm and that has spread to the local lymph nodes, tend to have a median survival time of 3 months, while dogs with stage 4 which has spread to the lungs, have sadly just a few weeks to months to live.

Of course, all of these are just numbers. Only your vet can help you figure out how fast the cancer may spread based on several individual factors such as the type of cancer, its stage and whether you have the financial resources to pursue fast treatment. In some cases, a consult with a veterinary oncologist can help provide better details.

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