Russian to English Medical Medical (general) Pathology

Dear colleagues,
In a pathology report there is a term I really don't understand.

"Фрагменты слизистой толстой кишки и фиброзированной основы с разрастаниями аденокарциномы."

Could it refer to the intestinal stroma?

Other guesses and context:
The actual fragment had a slice of colon with its mesentery. Could this term refer to mesentery?

The rest of the report has absolutely no mention of fibrotic changes in the tissue, also the tumor appearance is not fibrotic.

Any clues?
Thank you!