Angela,
It was just a stroke of luck I saw your post - I've not been paying such close attention to the forum lately. And I certainly wasn't expecting to see a question directed my way on this thread
It seems you in fact do NOT have progression, so for the time being anyway the pertuzumab is not an issue, is it? If they are making it an issue I think you could challenge that. Are they pushing you to go on Pertuzumab? At worst, the evidence of possible progression is inconclusive and needs to be clarified. At best, it is not progression, the TDM1 is working and you should not have to add the pertuzumab.
I still, from my perspective, do not fear pertuzumab. Everyone responds differently to any given therapy; one person will not respond or have terrible side effects where the next person might do fine. But with new combinations, it's especially hard to know.
I am in a different study than you are. I'm on TDM1 as a single agent, so have no other TDM1 options if it stops working. Maybe from that perspective, I'd view pertuzumab as a possible safety net, but I have been watching it anyway for quite some time.
In your study, I might look at it this way: you are on TDM1 and are doing well on it. If you have progression, that is a sign that you probably need to make some change - in your case, adding Pertuzumab or dropping from the trial to pursue other options. As long as the TDM1 is working, great! If it is not working well, you will have to make choices anyway.