What is osteosarcoma?⁠ It is a primary bone tumour that often affects dogs (especially large or giant breeds) and can manifest in the limbs, sometimes with rapid changes and associated pain or structural changes. ⁠ ⁠ Primary signs to watch out for:⁠ ⁠ ◽️Lameness or limping (often one leg)⁠ ◽️Swelling or pain - sometimes a lump at the site⁠ ◽️Decreased activity level or reluctance to engage in normal play or walks⁠ ◽️Unexplained weight loss and lack of appetite⁠ ◽️Behaviour changes - restlessness