Cancerous Cysts On Boxers. An infection, such as a bacterial infection or localized abscess, can appear as a mass on the gums. Fluid builds up inside the sac, causing a swelling on the surface of the skin.
But the main reason boxers are so susceptible to cancerous tumors is their genetics. Can a cyst on the gum be cancerous? Melanoma occurs more frequently in dogs with darkly pigmented skin.