Cancer can absolutely be that aggressive, and many of your internal organs don't have the sorts of pain and proprioception sensors we think of from our experience interacting with the world through our skin.
It's possible to have twenty small tumors throughout your body, causing no real issue, and then shortly thereafter they continue growing enough to impinge nerves, blood vessels, airways... And you're suddenly diagnosed with stage IV cancer.
It's possible to have twenty small tumors throughout your body, causing no real issue, and then shortly thereafter they continue growing enough to impinge nerves, blood vessels, airways... And you're suddenly diagnosed with stage IV cancer.