Fluorescent Tumor-seeking Nanoparticles
Nanoparticles small enough to travel through the brain without causing damage (33 nanometers wide) carry a peptide extracted from scorpion venom which features tumor-seeking abilities. Once the particle attaches to a tumor cell it becomes flourescent and thus, many times more easy to detect with a proper scanner, and eventually, easier to determine the boundaries of a tumor in case it needs extraction.
Now, these particles have only been tested in mice, but eventually, you could go for a regular full body check covered by your public health service, cause you never know where cancer may awake.
Source: Painting brain tumors with nanoparticles may help defeat cancer