Unfortunately, the answer is usually something along the lines of “We just don’t know” or the equally unsatisfying “It’s probably some combination of genetics, environmental factors, and bad luck.” There are times when a more specific answer can be offered. For example, with injection site sarcomas or cancers associated with retroviral (FIV and FeLV) infections, but those instances tend to be the exceptions rather than the rule.
In the future, veterinarians may be better able to answer the “why” question. Scientists at Colorado State University (my hometown University — go Rams!) have discovered a family of cancer-causing viruses in several U.S. populations of bobcats, mountain lions, and domestic cats, raising questions about whether these previously undetected viruses could be the root cause of some cancers found in housecats. According to a press release about the research:
Scientists tested nearly 300 individual blood samples from cats in three geographic regions in Florida, Colorado, and California [animal shelters across the United States collected and shared blood samples from domestic cats]. They found significant numbers of each species infected, indicating widespread distribution of the newly identified viruses, which are in the same family of gammaherpesviruses that can cause lymphoma and Kaposi’s sarcoma in people, especially those with HIV-AIDS and other immune-suppressing conditions.
It is not yet known whether the novel feline viruses are associated with diseases in bobcats, mountain lions, and pet cats, but the link between gammaherpesviruses and disease in other species clearly raises the possibility, scientists said.
“We think there’s a chance these viruses could be doing something similar in cats,” said Ryan Troyer, a research scientist in CSU’s Department of Microbiology, Immunology, and Pathology. “Discovery of viruses and virus transmission is important because it can help us understand common and emerging diseases in animals and people. That’s the first step to stopping infectious disease.”
The route of transmission remains unknown, but could occur when the animals fight in the wild, Troyer said. Interestingly, each of the three viruses was found predominantly in one feline species (the bobcat virus was also identified in some mountain lions). The domestic cat “version” was detected in 16% of samples from across all the study sites. Infected cats tended to be male and older than uninfected cats, which fits with the theory that fighting is an important mode of transmission.
The importance of this work remains to be seen, but the identification of three new feline viruses from a family known to cause cancer and other serious diseases in many species may help explain why some cats develop cancer and others remain healthy.