If you live with a pet, this can be a difficult question to think about. Animals become part of daily life - their routines, their personalities, the small changes you notice without really trying. So when health questions arise, it’s natural to want clear, calm information that doesn’t assume the worst.
Cancer is not limited to humans. It can affect companion animals too, particularly dogs and cats. But that doesn’t mean it’s inevitable, or that every change signals something serious.
How often cancer occurs in dogs, cats and other pets.
As veterinary care has improved, pets are living longer lives. With age, conditions linked to wear, repair, and cellular change become more visible - and cancer is one of them.
In dogs, tumours of the skin and soft tissues are most commonly identified, along with cancers of the mammary glands and lymphatic system. These often appear as lumps, swellings, or gradual physical changes rather than sudden illness.
In cats, a higher proportion of diagnosed tumours are malignant. Soft tissue sarcomas, mammary adenocarcinomas, squamous cell carcinomas, and lymphomas are among those most frequently seen. As with dogs, risk increases with age.
Importantly, not every lump or change is cancer. Many findings turn out to be benign. One reason cancer can be harder to recognise early is that it often looks very similar to harmless conditions at first.
How age and breed can influence risk
Cancer risk in pets isn’t evenly distributed.
Large population registries show differences by species, age, sex, and breed. Some dog breeds are more likely to develop specific cancers because of inherited susceptibility - not because of anything an owner has done. Size also plays a role, with larger breeds more prone to certain bone and soft tissue cancers.
In both dogs and cats, most cancers develop later in life. Time matters. The longer cells are active and repairing themselves, the more opportunity there is for things to change.
Why awareness matters
Understanding that cancer occurs naturally in pets helps explain why veterinary professionals sometimes suggest monitoring or investigation even when signs are vague or slow to develop.
Changes are rarely judged in isolation. They’re considered over time, in context, and alongside what’s normal for that animal. Earlier understanding isn’t about assuming the worst. It’s about clarity - having more time, more options, and a clearer picture of what’s going on.
That same principle is one reason naturally occurring cancers in pets have also helped improve understanding of cancer in people. Studying disease across species has expanded knowledge on how cancers develop, behave, and respond to treatment.
If something about your pet doesn’t feel quite right - a change that persists, progresses, or simply sits uncomfortably with you - it’s reasonable to talk it through with a veterinary professional. That conversation is about understanding, not jumping to conclusions.
References
Dhein ES et al. Incidence Rates of the Most Common Canine Tumors Based on Data From the Swiss Canine Cancer Registry (2008–2020). PLOS One, 2023.
Graf R et al. Swiss Feline Cancer Registry: Occurrence of Tumours in Cats in Switzerland (1965–2008). Journal of Comparative Pathology, 2015.
Fonti N et al. Factors Influencing Malignant Tumor Development in Cats: A Multicenter Retrospective Study. Scientific Reports, 2026.
Schiffman JD, Breen M. Comparative Oncology: What Dogs and Other Species Can Teach Us About Humans With Cancer. Philosophical Transactions of the Royal Society B, 2015.








.png)