is it possible to have a green and a brown eye?

My cat Punkin, cat on the right has a brown eye and a green eye. He was adopted so I don't know if he was born this way, however he has no signs of diacomfort, watery eyes, or more than one colour in a particular eye so I don't think its cancer.
I researched cat heterochimia online and noticed cats tend to have one blue eye and one other coloured eye, and have not come across the possibility of a green eye and a brown one. It seems multicoloured eyes is more common in white cats and could barely find anything about orange cats.
So is this a really rare genetic combination or is it cause for concern?

Heres another pic

I've never seen an eye look this way. It appears very dark, the whole thing, not so much as a different color but the eye itself doesn't look quite normal. While this might be perfectly healthy, if you haven't brought your cat to the vet yet it might be worth checking out.

Is there any "white" to the eye at all or is everything this dark color?

The reason I ask is because I've heard blue eyes --in humans anyway--are more predisposed to cancer due to the lack of melanin .

He has white if he rolls his eye to each side. He does have a noticeably darker pupil than the brown surrounding it , but it is a dark brown. His other eye is green.

I dunno... it doesn't look normal to me.  Have you asked a vet?  They should have the tools to examine the eye properly.