My Husband Has A Pus Sac In The Corner Of

My husband has a pus sac in the corner of his eye, we saw a doc this am, they think it might be cancer. What are the chances it is something else not so serious? They say it has blood vessels running thru it. It's about the size of a pencil eraser. Not very painful. Looks like a giant eye-goop sleeper at a glance.