Long term Treatment with Hercepton and Perjeta for HER2 Positive

I am due to finish Hercepton and Perjeta in Dec. These drugs  combined with the Chemo have killed the cancer in the breast and the lymph glands under the arm. Woo hoo!  I am having radiotheraphy to mop up the lymph glands in the neck and chest. My oncologist has now raised the issue of staying on these drugs longer, which wasn't what she said at the previous appointment. I will have a Pet scan at the end of the year to see if all the cancer is gone. So I am undecided whether to stay on the drugs or take a risk and go off them. I would like to hear any thoughts you have about this.
Many Thanks, I am always inspired by all of you wonderful people xxx