Targeted combination effective against metastatic BC

GlaxoSmithKline has reported positive data from the first randomised, multi-centre, open-label Phase III trial of the combination of two targeted agents, Tykerb (known as Tyverb in Europe; lapatinib) and Herceptin (trastuzumab), in women with HER2-positive metastatic breast cancer (BC).

In the study, 296 patients with HER2 (ErbB2)-positive BC who had documented progression on trastuzumab treatment in the metastatic setting were eligible to be randomised to receive lapatinib (1,000mg) plus trastuzumab (2mg/kg weekly after 4mg/kg loading dose) or lapatinib alone (1,500mg). Patients were heavily pretreated and had received a median of six prior anticancer regimens. Patients had received a median of three prior lines of trastuzumab. The primary endpoint of the study was progression-free survival (PFS), and secondary endpoints included clinical benefit rate, response rate and overall survival. If patients progressed on the lapatinib monotherapy arm after four weeks of therapy, they could cross over to receive the combination of lapatinib+trastuzumab.

Despite receiving multiple prior lines of anticancer therapy, patients who received lapatinib plus trastuzumab in this study experienced:

• a statistically significant increase in median PFS versus lapatinib alone (12 vs 8.1 weeks);
  a 27 per cent reduction in the risk of disease progression (hazard ratio [HR]=0.73; p=0.008);
• a response rate of 10.3 versus 6.9 per cent;
  double the overall clinical benefit rate versus lapatinib alone (24.7 vs 12.4 per cent; p=0.01); and
• a trend in improved overall survival (HR=0.75; p=0.106).
  The study also demonstrated the activity of lapatinib as a single agent in this patient population, with patients on this arm achieving a median PFS of 8.1 weeks and an overall clinical benefit rate of 12.4 per cent.

Adverse events were similar in both arms, with Grade 1/2 diarrhoea significantly higher in the lapatinib+trastuzumab arm (53 vs 41 per cent; p=0.03). Two patients in the combination arm and one patient in the lapatinib monotherapy arm experienced symptomatic decreases in left ventricle ejection fracture (LVEF); one patient in the lapatinib+trastuzumab arm died due to a pulmonary thromboembolism with progressive malignant pleural effusions; two patients with LVEF decrease later recovered. Isolated cases of asymptomatic transient decreases in LVEF were noted in both treatment arms.

Both treatments target the HER2 protein but work in different ways. Trastuzumab attaches to the outside of the HER2 protein, while lapatinib enters the cell to block signals from the HER2 protein for the cancer to grow. The clinical synergy of lapatinib and trastuzumab confirms previous observational findings in preclinical studies and previously reported data from a Phase I study. These latest findings confirm the rationale for further research of this combination in earlier lines of therapy in the metastatic setting and in early-stage disease. Additional analysis is under way to explore the benefit that lapatinib plus trastuzumab can offer to less heavily-pretreated patients.

Matthew Dennis - Editor, Cancer Drug News