The liver hopefully will not be cancerous. It can spread to there but usually the lungs or thereabouts is the first stop... So hopefully this is nothing. The other side node to me is more concerning. Just before I started rads I had a CT. The Rads dr. didn't readily give me the results even though I asked him at the time. Clearly he hadn't taken the time to look before meeting with me because he sent a resident out to look at them mid meeting and scared the shit out of me. (long story involving my lungs that after all the worrying turned out to be NOTHING) Anyway when asked about my head and neck CT he said it was just to plot my radiation. Imagine my dismay when he actually looked at my scans afterwards, and I got a call at home with him wanting to see me the next morning. Turns out those unimportant scans actually showed a small active node on the opposite side. Knowing that I was very gung ho and motivated he decided to radiate that side as well just to be on the safe side. I later asked my SO about the node - he said likely it wasn't cancerous... (based on location) But I was happy to have nuked it anyway.

It does jump the midline sometimes. Your brother is quite young and likely hypermetabolic. Hopefully they do something. Chances are he may have come down with something (that's what I think in retrospect as I had been in mexico at a resort literally three days before my scan. But better safe than sorry.

This cancer can be quite aggressive in younger people so making certain that any concerns are recognized and acted on is VERY important.
hugs