Cancer  is the leading cause of death in dogs, especially older dogs. However, it is not uncommon among younger dogs nowadays. But half of all cancers are curable, if caught early. The most common ones are malignant lymphoma, which is a tumour of the lymph nodes, and mast cell tumours, a form of skin cancer. There are mammary gland tumours, or breast cancer, and soft tissue sarcomas as well. Vets find bone cancer in dogs also fairly common. It is notoriously difficult to detect cancer early in pets. 

In many cases, cancer cannot be detected in blood. It is critical to remember that a pet can be very sick ‘inside’, without showing any of the signs outside, which is why regular veterinary checkups are highly recommended. Early detection is key when dealing with cancer.

The warning signs of cancer in dogs are similar to that in people — a lump or a bump, a wound that doesn’t heal, any kind of swelling, enlarged lymph nodes, a swelling in the bone, abnormal bleeding. These are all the classic signs. But sometimes, there are little or no signs, at least early on. So if at any time your pet isn’t feeling well or there’s something abnormal or not quite right, the owner needs to bring it to the attention of their veterinarian immediately.

There also seems to be a genetic component in some cancers, because according to the experts, there are some breeds who seem to be more prone to cancer than others. Golden Retrievers have a strong incidence of cancer. So do Boxers, Labrador, Retrievers and Bernese Mountain dogs. It shows that there are probably specific genetic components to some cancers. But it is still not proven and debates are ongoing of how much they are genetics versus environmental factors. As mixed-breed dogs come from a much larger gene pool, they would be less likely to get genetic-based cancers. But that doesn’t have to do anything for spontaneous or environmentally-caused cancers.

A majority of the cancers we see can be dealt with surgically. Many of these tumours — the mast cell tumours, a lot of skin tumours, soft tissue sarcomas — can be removed surgically and are cured. Even in situations where they have advanced to a lymph node, there are options that can prolong your dog’s life and even cure him. Radiation and Chemotherapy has become common. Good oral care can help decrease oral cancers.

The biggest thing is spaying your dog. If you spay a dog, you’ll reduce the chance of mammary cancer eight-fold in females and testicular cancer in male dogs, just because of the hormonal influence.But overall, prevention is difficult because we don’t know the causes of most cancers. Hence, rather than trying to prevent cancer, identifying it early and getting a quick treatment is a better strategy. 
Again, early detection is paramount. While there is no reason to be paranoid, stay informed, keep your eyes open.

Abnormal swellings 
The most obvious sign is a mass (or bump, or lump) that keeps growing under the skin. Have it removed and biopsied. If it is malignant or cancerous, then we can discuss what to do next.

Difficulty in eating
A lump in the neck could be putting pressure on the esophagus.
Weight loss
This means unexplained weight loss without any obvious cause. It could include a tumour along the intestine or a mass pushing along it. One of the first things a pet will then do is stop eating.

Breath and urine
This could be due to a mass putting pressure on the respiratory system, urinary 
system or digestive system.

Bleeding
Bleeding from the nose is a common sign. 
Reluctance to exercise or loss of stamina is another.