From memory: Clark noticed that one of his friends is sick, which then we discover is leukemia, and he xrays the room and finds a note after the kid is gone

It's a sad but beautiful story drawn in a Tim Sale style (I think) but I can't remember which is it for the life of me.

Would you please help me out? Thank your for your time and help

Ps. I'll try and remember as much as I can in the meantime