Can trastuzumab improve the outcomes of women with HER2 positive breast cancer?

This study explored whether trastuzumab (Herceptin) is an efficient drug for the treatment of HER2-positive breast cancer (BC) in patients who have previously received radiotherapy (RT) after breast removal surgery. The authors found that trastuzumab reduced the recurrence of BC and improved survival without cancer coming back.

Some BCs can have high levels of a protein called HER2 (human epidermal growth factor receptor 2) on their surface. These are called HER2-positive BCs. HER2 protein promotes the growth of BC cells. HER2-positive BCs tend to be more aggressive than HER2-negative BCs.

Common treatments for BC include the surgical removal of the whole breast affected by cancer (mastectomy), as well as chemotherapy and radiotherapy. Trastuzumab (Herceptin) is a type of targeted therapy that blocks the HER2 protein. Therefore, this drug stops the growth and spread of HER2-positive BC. 

While several studies showed the importance of trastuzumab for the treatment of early-stage HER2-positive breast cancer, little is known about the effectiveness of trastuzumab in patients that have received radiotherapy after mastectomy compared to patients with HER2-negative BC.

This study analyzed data from a previous clinical trial. The original clinical trial included 793 patients with BC who underwent a mastectomy followed by RT. Patients were separated into 2 groups. Group 1 included 547 patients who were HER2-negative. Group 2 included 136 HER2-positive patients who received trastuzumab. Group 3 included 110 HER2-positive patients who did not receive trastuzumab treatment. Patients were followed up for an average of 6.8 years. During this period, many patients from group 3 switched to group 2.

Patients in group 1 had a significantly lower recurrence rate at 5 years (6.8%) compared to group 3 (13.9%). Patients in group 1 also had a significantly lower rate of cancer spreading (metastasis; 22.4% vs 33.8%) and longer survival without disease (76.1% vs 61.9%) at 5 years compared to group 3. However, there were no significant differences in recurrence rate, metastasis, and survival without disease between group 1 and group 2. 

Patients in group 2 were significantly less likely to relapse and have cancer spreading compared to group 3. Patients in group 2 were also significantly more likely to have longer survival without disease compared to group 3.

The authors found that trastuzumab reduces the risk of relapse and improves the survival of patients with HER2 positive BC. The authors outline that trastuzumab treatment provides patients with HER2-positive BC similar survival without disease as in patients with HER2-negative BC. 

Patients in the trastuzumab group were not randomly assigned and could switch later on to receive this treatment. This could have affected the overall results.