Women with HER2-positive breast cancer had an improved rate of complete tumor disappearance in just 12 weeks when the monoclonal antibody pertuzumab was added to the standard therapy, consisting of trastuzumab plus the chemotherapy agent docetaxel.

In the phase 2 NeoSphere trial, 417 treatment-naïve women with early, locally advanced, or inflammatory HER2-positive breast cancer—an aggressive form of the disease—were randomized to one of four groups:

  • Group A (107 women) received trastuzumab plus docetaxel.
  • Group B (107 women) received pertuzumab and trastuzumab plus docetaxel.
  • Group C (107 women) received pertuzumab and trastuzumab.
  • Group D (96 women) received pertuzumab plus docetaxel.

After just four cycles (12 weeks) of treatment, nearly half the women in group B (49; 45.5%) had a significantly improved pathological complete response rate, compared with 31 (29%) of the women in group A, 23 (24.0%) of the women in group D, and 18 (16.8%) of the women in group C.

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In a statement describing the findings, which were published in The Lancet Oncology, lead study author Professor Luca Gianni, from the San Raffaele Cancer Center in Milan, Italy, pointed out that the Group C results were also notable in that a sizeable proportion of women achieved tumor eradication without the addition of chemotherapy (docetaxel), thus avoiding chemotherapy-associated toxicities.

“The tumor response time to this new triplet combination is one of the highest reported to date, despite just a short treatment time, and could be a big advance for women with HER2-positive disease,” affirmed Gianni. “Moreover, these findings suggest a potential future role for chemotherapy-free HER2-targeted therapy.”

The new triple-combination therapy was well tolerated and did not significantly increase side effects or cardiac risk compared with other regimens. The most common adverse events of grade 3 or higher were neutropenia (affecting 48 women in group B and 61, 1, and 94 women in groups A, C, and D, respectively), as well as febrile neutropenia (in 9, 8, 0, and 7 women, respectively), and leucopenia (in 5, 13, 0, and 7 women, respectively). The number of serious adverse events was lowest in group C (four events in 4.0% of patients), and similar in the remaining three groups (15-20 serious adverse events per group in 10% to 17% of patients).