Please Help - 8 yr old Cat w/ Sore on Head

This weekend we noticed our white/black *indoor* cat had a patch of
his hair missing from his head just over the right eyelid. It appeared
as a nail scratch from our other more agressive cat as they play fight
sometimes. I applied some peroxide on a q-tip to the area. The next
day, the area turned a pinkish/red color and grew to the size of a
dime. The area is flat, not raised or depressed, but it was becoming
bloody/crusty so I applied more peroxide on a q-tip. After only a
couple of days it seems to be moving down closer to his upper eyelid
but not yet there. We noticed new open wounds within that small area
that my wife thinks is the result of him scratching. I dont know if
it's a scratch, a growth, cancerous, eczema, etc. My question for the
vet will be, why is he scratching this - what is the underlying
condition?

I fear it may be some cancerous lesion, but my wife thinks it it just
the result of a scratch.

We will be bringin him to the Vet in a couple of days but any of your
expeiences/knowledge with the possibilities of this type of feline
skin irritation would be helpful.