Ado-trastuzumab emtansine (T-DM1) is an antibody-drug conjugate that incorporates the HER2-targeted antitumor properties of trastuzumab with the cytotoxic activity of the microtubule-inhibitory agent DM1. T-DM1 allows specific intracellular drug delivery to HER2-overexpressing cells, potentially improving the therapeutic index and minimizing exposure of normal tissue. The phase III EMILIA or TDM4370g (NCT00829166) study was a randomized, open-label trial enrolling 991 patients with HER2-overexpressing, unresectable, locally advanced or metastatic breast cancer who were previously treated with trastuzumab and a taxane.[Level of evidence: 1iiA]
Patients were randomly assigned between T-DM1 versus lapatinib plus capecitabine. Median PFS was 9.6 months with T-DM1 versus 6.4 months with lapatinib plus capecitabine (HR, 0.65; 95% CI, 0.55-0.77; P < .001). Median OS at the second interim analysis crossed the stopping boundary for efficacy (30.9 months vs. 25.1 months; HR, 0.68; 95% CI, 0.55-0.85; P < .001). The incidences of thrombocytopenia and increased serum aminotransferase levels were higher in patients who received T-DM1, whereas the incidences of diarrhea, nausea, vomiting, and palmar-plantar syndrome were higher in patients who received lapatinib plus capecitabine.
Further evidence of T-DM1's activity in metastatic HER2-overexpressed breast cancer was shown in a randomized phase II study of T-DM1 versus trastuzumab plus docetaxel.[Level of evidence: 1iiDiii] This trial randomly assigned 137 women with HER2-overexpressed breast cancer in the first-line metastatic setting. At median follow-up of 14 months, median PFS was 9.2 months with trastuzumab plus docetaxel and 14.2 months with T-DM1 (HR, 0.59; 95% CI, 0.36-0.97). T-DM1 had a favorable safety profile compared with trastuzumab plus docetaxel, with fewer grade 3 AE, (46.4% vs. 90.9%), AE leading to treatment discontinuations (7.2% vs. 40.9%), and serious AE (20.3% vs. 25.8%). Preliminary OS results were similar between treatment arms.
Patients whose tumors have progressed on hormone therapy are candidates for cytotoxic chemotherapy. Patients with hormone receptor-negative tumors and those with visceral metastases are also candidates for cytotoxic agents.
Single agents that have shown activity in metastatic breast cancer include the following:
- Albumin-bound nanoparticle paclitaxel (ABI-007 or Abraxane).[71,72]
- Alkylating agents.
- Vinca alkaloids.