Hi KK,
I had a similar response. My tumor measured 3.2cm on MRI & ultrasound but felt more like 7cm (I have still not received a great explanation as to why it felt so much larger). Either way, with AC, I felt noticeable shrinkage in both the tumor and lymph nodes. Unfortunately with Taxol, the size didn't change but the Oncologist assured me it was getting softer. I also asked about more AC or adding Carboplatin and they insisted that we needed to complete the original plan as even though the tumor wasn't shrinking, it also wasn't growing and the chemo could still be doing it's job. They described it as a cookie crumbling so even though the tumor is still there, the pathology might show that there are big holes in it.
My final pathology showed 2.1cm remaining but low cellularity (1% was invasive) so that is definitely a possibility for you. Sentinel lymph nodes were negative which I am told is important. Don't get discouraged...you're almost done with chemo!!