Picture two cocktail straws going through marshmallows: The straws, vertebral arteries and the marshmallows are tumors. One of the gifts/blessings is that Madison still has both vertebral arteries. Proton and chemo as suggested by MGH, did make surgery less invasive. Absent proton/chemotherapy, there would still be marshmallow cells on the straws.
Unfortunately DNA sequencing couldn't pan out, which speaks to the small amount of viable tumor remaining... good news of sorts news: Thing-1 and Thing-2 (tumor remnants) had their asses kicked.