Here are a couple of interesting articles about tumors in chickens:
https://thecountrysmallholder.com/poultry/tumours-in-chickens-8255996/
https://thisnzlife.co.nz/why-these-two-viruses-can-cause-your-chickens-to-get-cancer/
Adenocarcinomas of the oviduct and ovary is a very common cancer which occurs in a lot of hens over 2 years old. Those tumors differ from the lymphoid tumors seen in Mareks disease or avian lymphoid leukosis virus. Some differences in the two viruses, are that MD may show up after 5 weeks old...