Objectives A. Primary objectives: 1. To evaluate the safety of PSK when given with HER2 -directed immunotherapy . B. Secondary objectives: 1. To evaluate the effect of PSK on NK cell functional activity when given with HER2 -directed immunotherapy . C. Tertiary objectives: 1. To investigate the effect of PSK when given with HER2 -directed immunotherapy on: a. Serum of pro -inflammator y cytokine and/or chemokines. b. Intermolecular epitope spreading. c. Serum TGF -β levels. d. Progression free survival (PFS) and overall survival (OS). 5.