After 4 cycles of chemotherapy should a liver met start reducing in size ? is 16 mm classed large ?

Kinetics of response: Faster growing tumors tend to respond quicker, but tumors can be resistant. Typically 4 cycles of chemotherapy is enough time to know whether the disease is responding. Whether to continue treatment depends on the goals of care. Stable disease is better than progression, so more treatment may be fine if side effects are manageable. 16 mm is not large yet still represents millions of tumor cells.