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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Is The Cause of Cancer Really Not Known?

Updated: November 4th, 2019

Conventional vets (and I count myself among this group) suggest that the cause of cancer is not known.

Well, this statement rests on a faulty premise, because there is no single cause of cancer.  Cancer is the product of many separate steps that all must occur before the disease happens.



So of course the cause is not known, because of the use of the singular word “the”.

On a molecular level, you need certain changes in the DNA (genes). Then you need the body to not repair these changes, which is another separate problem.

Changes in DNA can result from:

  • environmental toxins (which, yes, we are all constantly bombarded with in Western living),
  • dietary substances in dog food and treats
  • radiation (from the neighboring star, the Sun),
  • viruses,
  • having parent(s) with the DNA problem
  • free radical excess in the body,
  • errors in the cell replication process in the body
  • altered pH

and more.


Get a copy of the Dog Cancer Survival Guide to learn more on cancer causes, and dog cancer


One the mutations occur in the DNA, you get errors in the genes that control the growth of cells.  So gas pedals get stuck in the “on” position and brake pedals are stuck “off”.

At this point the immune system is supposed to catch the new abnormal cells.  The often do, but sometimes not.  When the immune system is unable to catch and destroy the developing cancer cells, cancer happens.

Immune suppression is caused by many things as well:

  • a diet that has nothing to do with what a dog would eat in the wild
  • improper sleep/wake cycles
  • chronic stress
  • depression/lack of stimulation/lack of healthy, self-esteem building activities
  • lack of proper social network
  • improper intake of certain fats
  • obesity
  • a high level of inflammation in the body

and more.

This info taken from research in test tubes, petri dishes, and living bodies.

As you can see, the cause of cancer is not known. The causes of cancer are, however.  The ingredient is a fruit salad cannot be determined since fruit salads are, by definition, made of many fruits!

Dr Dressler


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  1. Helen Feher on November 29, 2021 at 8:16 pm

    My Golden retriever had a growth removed from his mouth. It was cancer. Since 2 months have passed his lymph nodes on his left jaw are the size of a softball. I’m scared it will choke him to death , He is eating good @ this time Our vet has him on predisone but lymph nodes are getting worse each day.. We have to help him somehow. He is 10 yrs old. I can’t beare to lose him. He is the best dog. Is there a med to help stop the swelling in the lymph nodes?
    Today is Nov 28, 2021. He needs help ASAP!

  2. Asbestos Cancer Mesothelioma on February 3, 2010 at 6:18 pm

    I think that so many things can cause cancer that we can not pin-point how someone got it. The air we breath causes cancer, what we eat, the chemicals we clean with. Everything.

    • Dr. Dressler on February 7, 2010 at 9:00 pm

      Dear Reader,
      I share this viewpoint in many ways. We live in civilization. Part and parcel of this choice and inevitability are the diseases of civilization. We are seeing the effects of modern society on our dogs as a reflection of ourselves on earth.
      Thanks for your thoughts,
      Dr D

  3. Prayers for our dog - Page 2 - SoWal Beaches Forum on June 28, 2009 at 1:05 am

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  4. Joyce DeLine on February 9, 2009 at 8:59 am

    I have a 12 1/2 year old female fox terrier. She has a walnut size tumor on her right lung. Because of its location a biopsy is not availiable without surgery. Her blood tests do not indicate any type of cancer elsewhere in her body. How invasive is the surgery for this type of tumor, recovery time and is it worth putting my dog trough this at her age!

  5. Debra Lawrence on February 2, 2009 at 10:18 am

    I’ve just receive the ultrasound which states: Liver:the liver is slightly large w/multiple focal lesions are rounded margins. Gall bladder is clean. Kidneys:Normal. Spleen:There is a large tissue dense mass in the tail region & many other smaller masses in the body of the spleen. UrinaryBladder:WNL. AdrenalGlands:WNL. Pancreas:No significant findings. IntestinalTract:WNL Normal bowel layering and motility. Sorocal Surfaces:WNL. Cursory Heart:NSF. Interpretation:1.Liver masses DDX primary vs metastatic neoplasia 2.Spleen DDX HSA vs hematopoeitic neoplasia vs other neoplasia vs other (fungagranuloma vs regeneration). Neoplasia is suspected. Consider biopsy of liver/spleen vs palliative Rx. The prognosis is guarded.

    • Dr. Dressler on February 8, 2009 at 11:34 pm

      Debra, this is not a good report, as I hope you have discussed with your vet. The odds of a cancer in the spleen that has already spread is high, I am sorry to say. You should discuss a biopsy with your vet to ascertain the type of cancer. If not, you should start going with diet, supplements, immune support etc. after discussing with your vet.
      D

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