Shih Tzus are not considered a high-risk breed for cancer overall. In a large UK study of pedigree dog deaths, cancer accounted for about 14.5% of Shih Tzu deaths, roughly half the 27% average across all breeds studied. That puts them near the bottom of the cancer mortality list, well below breeds like flat-coated retrievers, Bernese mountain dogs, and rottweilers, where cancer claims over 40% of deaths. But “lower overall risk” doesn’t mean zero risk, and Shih Tzus do face elevated danger from a few specific tumor types.
Overall Cancer Risk Compared to Other Breeds
Body size plays a major role in cancer risk among dogs. Larger breeds tend to develop cancer more often and die younger, while smaller breeds like Shih Tzus generally live longer and have a lower proportion of cancer-related deaths. In the same study that tracked over 15,000 pedigree dog deaths, Shih Tzus had a median age at death of 13.17 years, one of the longest lifespans recorded. Their 14.5% proportional cancer mortality was similar to other small breeds like dachshunds (16.7%) and German spitzes (16.3%).
When researchers looked at the age dogs are typically diagnosed with cancer, Shih Tzus fell into the later end of the spectrum. The overall median age at cancer diagnosis across more than 3,400 dogs was 8.8 years, and Shih Tzus were grouped with breeds like beagles and miniature schnauzers that tend to be diagnosed later than average. By contrast, breeds like boxers, Great Danes, and French bulldogs receive diagnoses significantly younger.
Mast Cell Tumors: A Notable Exception
While Shih Tzus have low cancer rates in general, mast cell tumors are one area of genuine concern. Mast cell tumors are among the most common skin cancers in dogs, and they range from low-grade growths that are easily treated to aggressive, high-grade tumors that spread quickly. Shih Tzus have a genetic predisposition specifically to the high-grade, more aggressive form. They share this risk with Shar-Peis, rottweilers, French bulldogs, and pit bulls.
Mast cell tumors typically appear as lumps on or just under the skin. They can look like almost anything, from a small bug bite to a raised pink mass, which makes them easy to dismiss. In breeds predisposed to aggressive forms, any new skin lump is worth having checked by a veterinarian. The distinction between a low-grade and high-grade mast cell tumor can only be made through a biopsy, but catching them early significantly improves outcomes.
Mammary Tumors in Unspayed Females
Shih Tzus are also listed among the breeds with the highest prevalence of malignant mammary tumors, alongside cocker spaniels, Maltese, poodles, and Yorkshire terriers. What makes the Shih Tzu’s risk particularly notable is the type of mammary cancer they tend to develop. In a study examining mammary carcinomas across these five breeds, 36% of the most aggressive subtype, called basal-like triple-negative tumors, came from Shih Tzus. These tumors are harder to treat because they lack the hormone receptors that some therapies target, and they tend to be higher grade.
Mammary tumors are overwhelmingly a disease of intact (unspayed) female dogs, and spaying before the first or second heat cycle dramatically reduces the risk. For Shih Tzu owners who have unspayed females, regular checks for lumps along the mammary chain, which runs along the belly, become especially important as the dog ages. Most mammary tumors in dogs appear after age 10.
Skin Tumors: Mostly Benign
Shih Tzus do develop skin lumps and bumps as they age, but the good news is these growths tend to be benign. A large Polish study examining thousands of skin tumors in dogs found that Shih Tzus had roughly half the odds of a skin tumor being malignant compared to mixed-breed dogs. Their odds ratio for malignant versus benign skin tumors was 0.47, meaning for every malignant growth, they developed proportionally more harmless ones. This doesn’t mean every lump can be ignored, but it does suggest that the average skin growth on a Shih Tzu is more likely to be a benign fatty tumor or cyst than something dangerous.
Lymphoma Appears in the Breed
Shih Tzus show up with some frequency in lymphoma studies. In one study of 77 dogs with lymphoma, Maltese and Shih Tzus together made up 26% of cases, the most commonly represented breeds. Lymphoma is a cancer of the immune system that often presents as swollen lymph nodes, typically noticed as painless lumps under the jaw, in front of the shoulders, or behind the knees. It can also cause lethargy, weight loss, and decreased appetite.
The treatment outlook depends heavily on how the cancer responds to chemotherapy. Dogs that achieve full remission had a mean survival time of roughly 565 days (about 19 months), while dogs that relapsed but responded to retreatment survived an average of over 1,000 days. Dogs that never responded to treatment survived only about 80 days on average. Canine chemotherapy is generally less aggressive than human protocols, and most dogs maintain a good quality of life during treatment with relatively mild side effects.
Practical Steps for Shih Tzu Owners
Given that Shih Tzus tend to develop cancer later than many breeds, researchers suggest that routine cancer screening for dogs of similar size and risk profile could reasonably begin around age 7, roughly two years before the median diagnosis age. For Shih Tzus, this aligns well with the shift into senior wellness visits that most veterinarians recommend.
At home, the most useful habit is regularly running your hands over your dog’s body to check for new lumps, skin changes, or swelling. Pay particular attention to the skin (where mast cell tumors appear) and the belly of unspayed females (where mammary tumors develop). Swollen lymph nodes, unexplained weight loss, persistent changes in appetite, and unusual lethargy are all worth a veterinary visit regardless of your dog’s age. Shih Tzus may not be a high-cancer breed as a whole, but the specific cancers they are prone to, particularly aggressive mast cell tumors and triple-negative mammary tumors, benefit enormously from early detection.