It is not unusual to receive mastectomy specimen post neoadjuvant therapy for advanced breast cancer.

One of pathologist role here is to assess the response of the tumor towards chemotherapy.

In my opinion, it is somehow not practical to use TNM staging even with prefix "y" for the post neoadjuvant staging. This is because the residual tumor is often broken into smaller tumor nodules, and according to TNM, the T designation would be the largest single residual tumor.

This probably does not reflect the treatment effect, given that multiple small tumor nodules would still be a big tumor burden. Therefore, the treatment effect would be overestimated using TNM staging for post neoadjuvant therapy specimen.

I try to follow the MD Anderson Cancer Centre method detailed in

http://www3.mdanderson.org/app/medcalc/index.cfm?pagename=jsconvert3.

This would be a good alternative for reporting mastectomy specimen post neoadjuvant therapy.