Cat's tumor removal incision still itching after almost a month?

My 11yo kitty had a mast cell tumor removed from his shoulder about a month ago. At about 10 days, he had the surface sutures removed, and the vet indicated there was at least one (maybe two, can't remember) layers of internal dissolvable sutures as well. The wound appears to be healing fine, but my kitty has been wearing a baby shirt for about two and a half weeks now to keep him from licking it.

I would think after this long he'd no longer be licking at it, but there's still one spot (the bottom of the incision) that he goes for within two minutes of taking the shirt off. He'll lick it raw and bloody if allowed (and quite quickly).

Does anyone have any experience with significant surgical suturing? Is this a reaction to the sutures? Would they still be dissolving, and possibly irritating him?

I've unfortunately found another suspicious mass (ugh) so we're heading back to the vet on Friday, but this has been bugging me and I was wondering if anyone else has experienced this. (I did mention it to the vet in an email about the new mass, but she didn't say anything about it, so maybe it's not a concern and I just need to be more patient?)

There could be some nerve damage from either the tumor or the surgery that is annoying him, but more likely it is itching him.  I can imagine if I were a cat I would certainly lick an itchy spot constantly.  You might mention this to your vet -- perhaps a cortison shot would help.  It's so hard since cats can't tell us if something hurts or itches or just tingles in an annoying fashion.  The literature on feline mast cell tumors DOES mention that they can actually cause a local allergic reaction if manipulated or bothered, so perhaps that is the problem here.

"If your cat suffers from cutaneous (skin) MCT, you may notice small, firm, raised, hairless nodules on the head, neck, trunk, limbs, or other sites on your cat. They can intermittently be itchy or red and self-trauma can cause ulceration. If a mass is manipulated or “bothered”, a local allergic reaction canensue, and you may notice significant redness and wheal formation in the area of the tumor. This is due to the release of histamine and other inflammatory substances. Typically cats with skin MCT are otherwise healthy and show no signs of systemic illness."

http://www.vcchope.com/resource-center/feline-mast-cell-tumors

Thanks! I'm going to bring it up with the vet, but really hoping it's just itching. Especially since the spot he goes for seems to be well below where the actual tumor was, but right where the suturing seemed a bit more complicated. He did mention when the surface sutures came out that it was possible there were some remnant mast cells that could cause irritation, but it was more likely that it was the sub dermal suturing that would cause itching. It's just that I didn't think the itching would last this long. (Though it didn't start until right before the skin sutures came out; prior to that, kitty left the incision area alone.)

And I've seen how an MCT can be bothered and cause a reaction, but that was specifically on the original tumor itself, not the surrounding area. The incision area doesn't look red or puffy or irritated in any way (except when cat licks it.) It's actually looked progressively more healed as time as gone on. 

Anyways, I was just hoping someone had experience with a surgical incision that was itchy even after mostly healed.

Bad news: my kitty has another mast cell tumor and thusly another round of surgery.

Good news (for the future reference of others): the vet aspirated the area of the original incision my cat had been licking, and there were no mast cells found there. The prolonged itchiness is just due to the sutures under the skin.