Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: There’s no good evidence that routine vaccines cause cancer in dogs. Injection-site sarcomas, tumors that form where injections were given, are a known but rare problem in cats, and are only very rarely reported in dogs. A small, temporary lump at the injection site is common and usually disappears within a few weeks. Any lump that grows or lasts should be checked.
Normal after vaccines
- A small, firm lump at the injection site that shrinks over a few weeks
- Mild soreness
- Mild tiredness for a day
When to have a lump checked
- It’s still there after about 3 months
- It’s larger than about 2 cm (roughly 3/4 inch)
- It’s growing a month or more after the injection
- It’s painful, hot, or draining
These guidelines come from feline guidelines but are a sensible rule for any pet. A quick needle test can identify most lumps.
Why cats are different
Cats have a well-documented risk of rare but aggressive tumors at injection sites, which is why cat vaccines are now given low on the legs or tail. This hasn’t been shown to be a meaningful problem in dogs.
Balancing risks
- Core vaccines protect against deadly diseases like parvovirus, distemper, and rabies.
- Vets tailor non-core vaccines to your dog’s lifestyle.
- Many adult core vaccines are given every 3 years.
More: what causes cancer in dogs.
Sources
- Ellis JA, et al. 2022 AAHA Canine Vaccination Guidelines. J Am Anim Hosp Assoc. 2022
- Hartmann K, et al. Feline injection-site sarcoma: ABCD guidelines on prevention and management. J Feline Med Surg. 2015
- WSAVA Vaccination Guidelines Group: Guidelines for the vaccination of dogs and cats
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.