How long can you stay on Enhertu for brain metastases?

I am stage 4 hormone receptors negative, hers2 positive metastatic breast cancer. I was diagnosed in December 2024 with stage 3. I had 6 cycles of chemotherapy (Herceptiin), double mastectomy and 5 weeks of daily radiation. I was told no cancer January 2026. March 2026, I started with headaches just in the morning and two weeks later in the hospital with severe headaches, dizziness, nausea and balance issues. I was told the cancer was back and on the brain. I have 4 lesions, which I had stereotactic radio surgery (SRS) radiation therapy and now on Enhertu infusion. I was told this past week that I will stay on the Enhertu until it is no longer working or my body doesn’t tolerate it anymore. Has anyone else had this diagnosis and treatment? How long have you been on it? How successful has it been?