What happened, in summary

A woman in her late 30s found a 2 cm lump in her left breast. Imaging showed 2 separate breast nodules and an abnormal axillary lymph node. Biopsy confirmed invasive carcinoma of no special type. Staging scans also found liver metastases and early spread to the spine, so the cancer was Stage IV, T2mN1M1. The disease was hormone receptor-positive and HER2-positive.

She began first-line treatment with docetaxel, trastuzumab, and pertuzumab. Docetaxel was given for 6 cycles, while dual HER2 blockade continued for 18 cycles in total. Anastrozole and monthly goserelin were added to suppress hormone-driven growth.

The cancer initially responded partially, but after about 12.6 months, new bone lesions showed that it was progressing. Treatment then changed to ado-trastuzumab emtansine, also called T-DM1, given every 21 days.

A PET scan after 7 cycles of T-DM1 showed a complete clinical and radiological response. The response continued through repeated follow-up and was maintained for about 3 years. She remained on T-DM1 with a sustained complete response for 41 months and 60 cycles. Her only significant toxicity was mild grade 1 anemia, and repeated heart scans found no cardiotoxicity. Because the cancer had been metastatic at diagnosis, treatment and imaging follow-up continued despite the complete response.

The response included disappearance of active breast, liver, and bone findings on imaging. T-DM1 continued because it was controlling cancer that had been metastatic from diagnosis. The complete response came after earlier progression on standard first-line HER2-directed treatment.