I've been googling this but getting very little results, other than that Stan Lee Vanity fair interview.
What I'm looking for is an explanation of:
* WHY, in his solo title, did Ben start to mutate further?
* HOW was this resolved? It suggests it continues in the Avengers book, but he just ducks out of joining them, then turns up in the FF. It seems like a strange subplot that "fell between the cracks" of titles folding and editors changing.
I thought it had to do with his extended stay on Battleworld, but, it has been so long since reading the old Thing series I'm not sure if that was the given explanation. It might have had something to do with his confrontation with the Beyonder during Secret Wars 2. That explanation is tickling the dusty halls of my memory. I could be wrong, tho.