Cancer is the leading cause of death in dogs over age 10, and early detection dramatically improves welfare outcomes, yet many cancers go undetected until advanced stages due to inadequate screening and subtle early signs.
Cancer causes welfare impacts that begin well before diagnosis because the early signs are subtle and easily attributed to normal aging. A dog with early osteosarcoma experiences bone pain for weeks or months before the lameness becomes severe enough to prompt veterinary attention. Lymphoma causes gradual fatigue and reduced appetite that owners may normalize. The welfare gap between early and late-stage diagnosis is enormous — early-stage cancers treated promptly can provide months to years of good quality life, while advanced cancers often require palliative care focused on comfort rather than cure. Prompt investigation of any behavioral or physical change in senior dogs is one of the most welfare-positive actions owners can take.