A new antibody-based treatment may offer women with early-stage HER2-positive breast cancer an alternative to traditional chemotherapy. In a recent trial, about 98% of patients receiving the new drug were alive and cancer-free three years after treatment, similar to standard chemotherapy. However, the side effects were notably less burdensome: women receiving the new drug experienced far less nerve damage and almost no hair loss. The treatment, called trastuzumab emtansine, belongs to a newer class of medicines designed to deliver cancer therapy more precisely.
Breast cancer comes in many forms. About one in five breast cancers are HER2-positive, a subtype driven by an overactive protein that accelerates tumor growth. Targeted therapies against HER2 have transformed outcomes over the past two decades. This new drug builds on that progress, using an antibody to deliver direct treatment to cancer cells.
The ATEMPT trial compared this new treatment with the standard treatment and found that while overall side effects were similar, the types of side effects differed, leading some women to prefer the newer drug.
A History of HER2-Positive Breast Cancer Treatment
The development of trastuzumab, a monoclonal antibody targeting HER2, dramatically improved outcomes for patients with HER2-positive breast cancer. Combined with chemotherapy, it significantly reduced cancer recurrence and death. For patients with small tumors that had not spread to the lymph nodes, 12 weeks of paclitaxel plus trastuzumab, followed by trastuzumab alone, became widely adopted after the APT trial showed a 10-year overall survival rate of 94%, breast cancer-specific survival rate of nearly 99%, and a 10-year recurrence-free rate of 96%.
Yet paclitaxel carries side effects, including nerve damage, hair loss, and reduced blood cell counts, which increase fatigue and infection risk. As more patients live longer after treatment, reducing side effects has become increasingly important.
T-DM1 represents a more targeted approach. It links trastuzumab to a chemotherapy drug, delivering treatment directly to HER2-positive cancer cells while limiting exposure elsewhere. In higher-risk early-stage settings, T-DM1 has already demonstrated efficacy. ATEMPT tested whether it could replace standard chemotherapy in lower-risk, stage I disease.
Inside the Trial
The ATEMPT trial enrolled nearly 500 patients across the United States. Participants received either T-DM1 every three weeks for a year or the standard treatment of paclitaxel and trastuzumab. Researchers tracked cancer recurrence or death and monitored complications that required delaying or stopping treatment.
After three years, about 98% of patients receiving T-DM1 were alive and cancer-free, compared with 94% on standard therapy. Altogether, the results suggest that T-DM1 may offer a slight edge in preventing recurrence, but with a distinct side-effect profile.
Overall rates of side effects were similar: 46% in the T-DM1 group and 47% in the standard therapy group. However, patients receiving paclitaxel were more likely to develop nerve damage, hair loss, low white blood cell counts, infusion-related reactions, and diarrhea. In contrast, T-DM1 more often caused low platelet counts and liver changes. Seventeen percent of patients stopped T-DM1 early due to side effects that triggered trial safety rules, compared with 6% on standard therapy. Many of those who discontinued T-DM1 continued treatment with trastuzumab alone to finish the planned year of therapy.
Patients receiving T-DM1 reported meaningful differences: less nerve damage, less hair loss, and better work productivity, particularly during the first 12 weeks when standard therapy patients were undergoing chemotherapy.
While the trial was not designed to determine treatment superiority, the results show that T-DM1 achieves high cancer-free survival rates with different side effects.
Implications for Patients and Clinicians
The ATEMPT trial does not replace the current standard of care. However, the findings expand the range of evidence-based options available for patients and doctors. Even with similar overall toxicity, T-DM1 may offer more manageable side effects, especially for those hoping to avoid nerve damage or hair loss. Conversely, T-DM1 is more expensive and carries risks of liver problems and low platelet counts.
The study reflects a broader trend in oncology: as survival rates improve, treatment decisions increasingly incorporate patient preference. Future research is exploring shorter courses of T-DM1 to maintain efficacy while reducing discontinuation rates and cost. Longer follow-up from ATEMPT will help clarify whether these early outcomes remain durable.
The Future of Targeted HER2-Positive Therapy
HER2-targeted therapy has transformed this once high-risk subtype into one with favorable outcomes. The next challenge is improving quality of life alongside survival. By expanding the conversation beyond survival to include individual priorities, studies like ATEMPT signal a more personalized future for cancer care, where good outcomes and patient experience are equally valued.
