breast cancer resistance to chemotherapy

Hello,

The  large breast cancer tumor (LABC) shrunk noticeably after the first session of ACT chemotherapy and the doctor said that lymph node cancers have been disappeared which was a very good news BUT the tumor hasn't shrunk after four sessions of AC and one session of T! (done every two weeks).
I'm wondering what's the reason for the tumor not shrinking? Does it resist to the therapy? Why  didn't it resist the first session?

Is it possible/common that the tumor is a combination of cancer and non-cancer cells?
What are the other options if it shows resistance to chemotherapy? Changing the drugs?

Thanks
nika

[Cleveland Clinic]

Dear nika:  It is possible that the tumor has developed resistance this chemotherapy if the tumor has not shrunk further.  However, without evaluation, it is impossible to determine this via the internet.  You should discuss this with your oncologist who can better determine next steps based on your particular situation.