What systemic therapy would you choose for elderly patients with HER2+ breast CA who have early metastatic relapse (within months) of completing adjuvant trastuzumab/paclitaxel?

Yes, even our frail older patients may have pretty aggressive HER2+ cancers. I am treating a lovely older lady who is on her 6th line of therapy and has responded to everything she's had, so far! We've been working together for about 7 years! Initially, I stuck to pretty standard regimens with dose ...