Osteosarcoma Metastasis to the Intestine in Dogs: What Owners Should Know

Paul, a retired physician, shared the case of his 13-year-old female lab/collie mix. She was diagnosed with osteosarcoma of the right humerus five weeks earlier. A chest x-ray showed no metastasis. The dog is receiving comfort care: gabapentin 600 mg every 8 hours, tramadol 50 mg two to three times daily, and carprofen half a tablet twice daily.

One day ago, the dog developed liquid stools and some red blood spotting. Paul stopped the carprofen and began Pepcid 20 mg twice daily. The dog still has a wonderful appetite and no vomiting. Today she passed a formed stool with red streaks. Paul asks: Does osteosarcoma metastasize to the intestine?

Understanding Osteosarcoma Spread in Dogs

Osteosarcoma is an aggressive cancer. In dogs, 80% of metastases occur in the lungs. (1) While it is not impossible for the cancer to spread to the intestine, the liver and spleen are the most common secondary sites. The bleeding Paul observed is most likely caused by one of the medications or a combination of them.

Stopping carprofen was a proper step. That drug is the most probable cause of the bleeding, as 70% of dogs treated with carprofen had mild to moderate punctate intestinal erosions. (2)

Gabapentin may also contribute, but its side effect is most likely gastric erosions. (3) Erosions in the stomach lining would typically appear as melena (black stool), not the red streaks described.

Tramadol can also cause gastric ulcers. (4) As with gabapentin, however, melena would be more likely; tramadol more commonly causes other GI symptoms such as constipation in dogs, not blood on the stool.

Should You Stop Giving Your Dog Her Medications?

The main question is whether to stop any of these medications because of side effects. Osteosarcoma is painful in humans, and we assume the same for dogs based on their behaviors. Pain from cancer can lead to aggression, fearful behavior (including fear biting), house soiling, lethargy, and many others. (5)

As Paul knows, these medications do not treat the cancer, but they can help maintain a good quality of life for the next few months.

Consider Talking to Your Vet About Reduced Dosages

For most dogs that have problems with NSAIDs like carprofen, a smaller dose (such as 1/4 tablet) may help without causing the bleeding seen here.

If the bleeding starts again, I would take my dog off carprofen but continue the other medications.

Sources

(1) Wilk, S. S., & Zabielska-Koczywąs, K. A. (2021). Molecular Mechanisms of Canine Osteosarcoma Metastasis. International journal of molecular sciences, 22(7), 3639. i.nlm.nih.gov/pmc/articles/PMC8036641/

(2) Mabry, K., Hill, T., & Tolbert, M. K. (2021). Prevalence of gastrointestinal lesions in dogs chronically treated with nonsteroidal anti-inflammatory drugs. Journal of veterinary internal medicine, 35(2), 853–859. i.org/10.1111/jvim.16057

(3) Aydin, S., Donertas, B., Kilic, F. S., Oner, S., & Kaygisiz, B. (2016). PT670. Antiinflammatory and gastric side effect of gabapentin. International Journal of Neuropsychopharmacology, 19(Suppl 1), 44–45. i.org/10.1093/ijnp/pyw044.670

(4) Järnbert-Pettersson, H., Andersson, M. L., Bilén, K., Broström, O., Lindh, J. D., & Mannheimer, B. (2019). Is tramadol associated to bleeding peptic ulcer? A nationwide case-control study in hospitalized Swedish patients. PloS one, 14(4), e0215356. i.org/10.1371/journal.pone.0215356

(5) Camps, T., Amat, M., & Manteca, X. (2019). A Review of Medical Conditions and Behavioral Problems in Dogs and Cats. Animals: an open access journal from MDPI, 9(12), 1133. i.org/10.3390/ani9121133

This article is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from your veterinarian. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

Osteosarcoma Metastasis to the Intestine in Dogs: What Owners Should Know