Depending on whether this is colonoscopy or histologic examination, you can phrase it as:
There is evidence that this cancer (or even tutor cells) inflitrated the muscularis mucosae layer.

OR

[More specifically, naming the procedure like colonoscopy] revealed that the cancer reached and invaded the muscularis mucosae layer.

OR

The examination (e.g. histology) revealed tumor cells invading the muscularis mucosae layer.

Take your pick depending on the specific context. Important: don't use "neoplasia" because -- although medically correct -- it is not that commonly used in English. Simply saying "cancer" is more common.