Chemo side effects - Don't fear the worst

Hello Can anyone tell me why I have to have chemo with Herceptin. None of my nodes were positive and my pet scan clear. As I am HER2 positive I know I that need Herceptin which is licensed to go with chemo. Why can't I just have the Herceptin on its own? Why compromise my immunity? Any ideas? Thank you Cathy

Hi anyone fearing chemo
I was diagnosed with BC 1st October and had 1st session of Herceptin and FEC yesterday.
First part of day was having portacath inserted and 2 hours later the Herceptin - promptly fell asleep. Woke just before the chemo started and although couldn't help thinking how can I  be so calm whilst having poison infused into me Kim my nurse was chatting all the way through. All finished feel asleep again…