Tumor at the spine condition are not stable

This is my 5th chemotherapy. My CEA are dropping very well from 3000 to 600 now. I have no pain on my lung all this while however the tumor at my spine are hurting my knee. Now after the every treatment I realize during the 4th day of chemotherapy rest week, I can feel the tumor minor pain again. Does that mean that the medicine are not working on my tumor?