Hard smelly lump INSIDE gut of chickens?

[K7S10]

I picked up some 2 yr old layers from some guy today for $1 each and butchered them.
I've done several butcherings before (mostly my own birds), but never come across this before.
When we gutted the birds, we found that two of them each had a fairly large, ovalish, hard mass inside. It was not attached to anything. They were yellowish and wrinkly. Cutting one open, there was a horrid smell inside and it was kind of darkish and crusty with some of it hollow. Unfortunately, I didn't have my camera with me to take a picture to show you. I didn't know if it was some kind of cancerous growth or what. Any of you come across this before? What did you do?

I ended up just tossing the birds out, just in case. Kind of maddening after going to the trouble of plucking them out in the cold wind though. Ah, well. Our freezer is well stocked now with the makings of soup!

 

[Sparrow]

Were they where you might expect to find an old retained egg or something?

 

[K7S10]

Thanks for pointing me in the right direction.
I sure wouldn't have thought egg, it was rock hard and partly hollow. But I spend an hour and a half yesterday morning looking through backyardchickens and found lots of info on retained eggs, 'lash eggs' and ovarian tumours. It sure looked similar to some of those photos. One person said: "It's made up of yolks and solidified infection. Over time it just gets larger and larger and because it's basically an infection, it goes systemic and kills the hen. It blocks the oviducts and as yolks keep coming down the duct, they can't go anywhere.
If you've ever dealt with bumblefoot, which is a staph infection, you see that the pus becomes cheesy and solid. Same with this, but it's inside the abdomen and oviduct."

Yuck.

Well, I'm glad I tossed the birds.