Lung Cancers in Dogs


Lung cancer

Question: Dear Dr. Mike,

My twelve year old shepherd mix female, BeniHana, was diagnosed last week with a malignant tumor on her left lung about 4" by 5". It was aspirated to confirm its malignancy but we do not know what type of cancer it is. My feeling is that it wouldn't be sensible to attempt to treat it with surgery, chemo, and/or radiation. My vet didn't want to sway me one way or the other, however, and I wondered what you thought. Surgery sounds highly invasive and painful and likely not very practical. My vet did say we could give her prednisilone (reduce inflammation) and lasix (fluid reduction), however, as a palliative approach. My questions are these: 1. What range of time has she got left (without any interventive treatment)? 2. She only coughs occasionally (it started about six weeks ago)--what other symptoms should I look for to determine how she is faring? 3. Last night, as she slept I noticed fast breathing and her heart, which has been shoved over by the tumor, was visibly beating against her chest cavity. I measured its rate to be about 126/minute. Is this anywhere normal for a 48 lb. dog? If not, what causes the very rapid rate? 4. I am very concerned about her comfort level, and I want to do the right thing. This is very hard emotionally for me, and probably physically for her. She still eats well and drinks large quantities of water. When is the time right to consider euthanasia? I really don't want her to to have endure much suffering. She already has endured years of painful hip dysplasia. 5. How common is lung cancer in dogs? Without knowing what type of cancer it is, can I know whether it can readily metastisize?

Thank you so much.


Answer: Wendy-

I am sorry, but it isn't possible to tell you much about the expected behavior of a tumor without knowing what type of tumor it is. Sometimes the only way to really identify a tumor is to remove it, or to at least obtain a piece of it surgically, so that a pathologist can examine the architecture of the tumor for clues as to what it is. This happens most frequently when cell types have lost most of their identifying features, making a needle biopsy sample inconclusive. That is a bad sign, usually indicating a higher tendency towards malignancy and rapid growth, but beyond that it is isn't possible to say much.

Coughing can be evaluated by frequency, harshness and productivity (what comes up during the coughing episode). Very frequent coughing, deep harsh coughing and the production of excessive amounts of phlegm, or other substances such as blood, are signs that a lung problem is worsening. Tiring readily, weight loss and unexplained fever occur with malignant tumors when they begin to really use a lot of the body's energy. Anemia is a frequent problem when malignant tumors are present and monitoring for it can be helpful in determining if the tumor is causing more problems than are visible. This is particularly true of tumors such as hemangiosarcoma, which can cause internal bleeding.

126 beats per minute could be within the normal range for a sleeping dog of her size, depending on what part of the sleep cycle she is in. Dogs have REM (rapid eye movement) sleep, which is when dreaming occurs in people, and heart rates can get high during this phase of sleep. The normal heart rate for dogs that are awake ranges from 70 to 180 bpm, with small dogs having higher heart rates and larger dogs slower rates, so this heart rate is not out of the normal expected range when awake. I couldn't find specific expected heart rate ranges for sleeping dogs.

I think it is a really good idea to consider pain relief medications, even if you are not currently seeing signs of pain. Carprofen (Rimadyl Rx) and etodolac (Etogesic Rx) are good initial choices. If there are signs of visible pain it may be better to use narcotic pain relievers such as morphine or fentanyl (available as Duragesic Patches Rx). It is reasonable to presume that some pain is present when there are malignant tumors and these would help with the arthritis, anyway.

Most dogs that are reaching the point where they are no longer able to enjoy life much stop eating, or have drastic reductions in appetite. They may refuse to play or to interact with their friends. In extreme cases, they may be totally inattentive to urinary habits or bowel movements, losing all pretense of normal household behaviors or not even moving away from a urine puddle or bowel movement. Almost all pet owners have enough empathy with their pets to recognize the time when their pet has given up fighting an illness. There is just a time when you stop wondering if the time is right to consider euthanasia and you just know that the time has arrived.

Primary lung cancer (cancer coming from lung tissue) is rare in dogs, so the odds are very high that a tumor seen in the lungs is a metastasis from a tumor somewhere else. This is not always the case but it is a reasonable presumption. So in most cases, just seeing a tumor in the lungs is reason to suspect metastatic cancer.

It may be worth asking your vet for a referral to a veterinary oncologist (cancer specialist) or internal medicine specialist, just to hear what the options are for identifying the tumor and treatment. You may decide that it isn't something you wish to pursue but you would have a better idea of what the potential for treatment and the prognosis would be. Sometimes knowing those things is worth making a trip to a specialist. On the other hand, if you are certain that you do not wish to pursue surgery, chemotherapy or radiation therapy then knowing the exact type of tumor and the prognosis is not quite as important. In that case, just treating the symptoms as they come along and providing good nursing care until BeniHana lets you know she is too uncomfortable to be happy may be the best option. Your vet can help with the palliative measures you mentioned and with pain control.

Trying to keep things interesting and giving in the temptation to spoil BeniHana some with special foods or activities can make her life much more enjoyable, despite the physical problems that might develop due to the tumor.

Mike Richards, DVM 11/4/2000


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...