An enlarging lump

Just as on yourself, if your dog has a lump that’s getting bigger or changing in shape or texture (especially if there are multiple lumps), you should see your vet. He or she will probably want to take a biopsy.

Swollen lymph nodes

Lymphoma is a kind of cancer that can cause lymph nodes (located throughout the body but most easily detected behind the jaw or knees) to swell. While other illnesses commonly cause this as well, if you notice swollen lymph nodes, you should always take your dog to the vet. Anything that causes swollen lymph nodes needs to be treated. If your vet suspects cancer, however, he or she will likely recommend a biopsy or cytology of the enlarged gland.

Chronic weight loss

Unless your vet has your pup on a diet, weight loss isn’t a good sign. The good news is that loads of things can cause your precious pooch to lose weight, but many cancer patients (human and otherwise) do experience weight loss.

Abdominal distension

If your dog’s belly rapidly becomes enlarged, it’s possible there’s some sort of mass (i.e., tumor) in the abdomen, or it could be a sign of bleeding in the area. Don’t confuse this with slow swelling of the abdomen, which likely indicates you’ve been overfeeding Fido. Your vet will probably order a radiograph or ultrasound.

Unexplained bleeding or discharge

If you see any unexplained bleeding from the mouth, nose, vagina, penis or gums, you should have your dog examined by a vet. It’s possible this could be due to some sort of trauma, so think about what you and your dog have been up to that could lead to an injury like that. It’s also possible that if your animal is still a puppy or very young, it’s a bleeding disorder of some kind. If you see any discharge you can’t explain, that could also be a sign of trouble. In any case, a vet needs to make the determination, especially if your dog is older.

Cough

There are a lot of reasons dogs cough (just like there are a lot of reasons we cough), but if your dog suddenly develops a dry, non-productive cough it just can’t shake, you should have it checked out as that’s a possible sign of lung cancer. The vet may need to do chest radiographs.

Chronic vomiting or diarrhea

Tumors in the gastrointestinal tract can cause chronic vomiting and/or diarrhea. As with all the other symptoms listed here, other things can also cause this, but you should always have the symptoms checked out because nothing causing them is good. A vet may order a radiograph, endoscopy or ultrasound to check for any tumors.

Straining to urinate

Generally, straining to urinate or blood in the urine indicates nothing more than a common urinary tract infection. That said, if it can’t be controlled with antibiotics or if it keeps coming back, it’s time to make sure your dog is checked for bladder cancer. There are several tests your vet may do, one of which is a cystoscopy that allows the doctor to do a proper biopsy for a definitive diagnosis.

Oral odor or other issues

Oral tumors may cause oral odor, cause your dog to begin preferring softer foods or even change its chewing habits (of course, so can poor dental hygiene or just getting old). Either way, if you notice strange food habits or a foul odor (especially in a dog that’s not that old) in a dog whose teeth you’ve taken care of, you should take your dog to the vet. The doctor may do several different types of tests, some of which may require sedation.

Lameness or evidence of pain

In older dogs, it’s not uncommon for them to develop joint issues, but if your dog develops sudden or unexplained lameness or seems to be in constant pain, you need to have it checked out. It could be a sign of bone or some other cancer. A vet will do radiographs if necessary to determine the cause of the issue.