Dual HER2 Blockade Along with an Aromatase Inhibitor is an Effective Chemotherapy-Sparing Alternative Treatment in Advanced Breast Cancer

SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. Approximately 266,120 new cases of invasive breast cancer will be diagnosed in 2018 and about 40,920 women will die of the disease. The HER or erbB family of receptors consist of HER1 (EGFR), HER2, HER3 and HER4. Approximately 15-20% of invasive breast cancers overexpress HER2/neu oncogene, which is a negative predictor of outcomes without systemic therapy. Approximately 50% of HER2-positive breast cancers are Hormone Receptor positive.

Patients with HER2-positive metastatic breast cancer are often treated with anti-HER2 targeted therapy along with chemotherapy, irrespective of hormone receptor status, and this has resulted in significantly improved treatment outcomes. HER2-targeted therapies include HERCEPTIN® (Trastuzumab), TYKERB® (Lapatinib), PERJETA® (Pertuzumab) and KADCYLA® (ado-Trastuzumab emtansine).

Dual HER2 blockade with HERCEPTIN® and PERJETA®, given along with chemotherapy (with or without endocrine therapy), as first line treatment, in HER2 positive metastatic breast cancer patients, was shown to significantly improve Progression Free Survival (PFS) as well as Overall Survival. The superior benefit with dual HER2 blockade has been attributed to differing mechanisms of action and synergistic interaction between HER2 targeted therapies. Not all HER2-positive, Hormone Receptor positive metastatic breast cancer patients, are candidates for chemotherapy. These patients however may benefit from anti-HER2 targeted therapy given along with endocrine therapy.

Preclinical evidence suggested that endocrine resistance may be related to cross talk between HER2- and Hormone Receptor-signaling pathways. HER2 inhibition may in turn enable the Estrogen Receptor (ER) to become the primary driver of cell proliferation, resulting in relative resistance to anti-HER2 therapy. Therefore, targeting both HER2 and ER simultaneously may be essential to derive optimal benefit among patients with HER2-positive Hormone Receptor positive metastatic breast cancer. Previously published studies demonstrated improved median PFS when single HER2 blockade combined with endocrine therapy was compared with endocrine therapy alone, among treatment naïve patients with HER2-positive and Hormone Receptor positive metastatic breast cancer.

Based on the improved outcomes with dual anti-HER2 blockade compared with single HER2 blockade in both neoadjuvant as well as metastatic settings, this present study was designed to evaluate the superiority of dual HER2 blockade with TYKERB® and HERCEPTIN® given along with an Aromatase Inhibitor (AI), over single HER2 blockade with HERCEPTIN® given along with an AI, in patients with HER2-positive, Hormone Receptor positive metastatic breast cancer, who experienced disease progression after prior neo(adjuvant)/first-line HERCEPTIN® based chemotherapy. This study also included a third treatment arm of TYKERB® plus an AI, which was compared with the other two treatment groups.

The ALTERNATIVE study is an open-label, phase III trial, in which 355 patients were randomly assigned in a 1:1:1 ratio to receive either TYKERB® along with HERCEPTIN® plus an AI (N=120), HERCEPTIN® plus an AI (N=117) or TYKERB® plus an AI. TYKERB® was administered at 1000 mg orally daily in the dual HER2 blockade group and at 1500 mg orally daily in the TYKERB® plus AI group. Patients receiving TYKERB® were urged to initiate treatment with Loperamide at the onset of diarrhea. HERCEPTIN® was administered IV at a loading dose of 8 mg/kg, followed by the maintenance dose of 6 mg/kg IV every 3 weeks. Physician’s choice of AIs included either Letrozole 2.5 mg, Anastrozole 1 mg or Exemestane 25 mg, orally daily. Enrolled patients were postmenopausal women, with histologically or cytologically confirmed ER-positive and/or Progesterone Receptor-positive, HER2-positive metastatic breast Cancer, as determined in a local laboratory. Prior treatment with endocrine therapy and disease progression during or after a prior HERCEPTIN® based chemotherapy regimen in the neo(adjuvant) setting and/or in the first-line metastatic setting, was a requirement for enrollment in this study. Only one prior regimen in the metastatic setting was allowed. Patients for whom chemotherapy was felt appropriate per treating physician’s judgement, were excluded from the study. Two thirds of the patients had received HERCEPTIN® based regimens in adjuvant setting and approximately one third in metastatic setting. The Primary end point was Progression Free Survival (PFS) with dual HER2 blockade plus AI compared with HERCEPTIN® plus AI. Secondary end points included PFS comparison of other treatment groups, Overall Survival, Overall Response Rate (ORR), Clinical Benefit Rate and Safety.

The study met its Primary end point and the median PFS utilizing dual HER2 blockade with a combination of TYKERB® along with HERCEPTIN® plus an AI was 11 months, compared with 5.7 months for HERCEPTIN® plus an AI (HR=0.62, P=0.0064). This represented a 38% reduction in the risk of disease progression. The PFS benefit was consistently observed in various predefined subgroups of patients. Further, the ORR and Clinical Benefit Rate were superior in the TYKERB® along with HERCEPTIN® plus AI group compared to HERCEPTIN® plus AI group ((31.7% versus 13.7% and 41% versus 31%, respectively). Although survival data were immature, there was also a trend favoring treatment with dual HER2 (median 46 months versus 40 months). When other treatment groups were compared, the median PFS with TYKERB® plus an AI was 8.3 months compared to 5.7 months with HERCEPTIN® plus an AI (HR=0.71, P=0.036), suggesting that among HER2-positive, Hormone Receptor positive metastatic breast cancer patients, who had progressed after prior treatment with HERCEPTIN®, anti-HER2 treatment with TYKERB® along with an AI may be a reasonable alternative, although this hypothesis will need to be confirmed. Common adverse events included higher incidence of diarrhea and rash in the groups treated with TYKERB® and serious adverse events were similar across the three treatment groups. Treatment discontinuation due to adverse events was lower in the dual HER2 blockade group.

The authors concluded that dual HER2 blockade with a combination of TYKERB®, HERCEPTIN® and an Aromatase Inhibitor (AI) resulted in improved PFS compared with HERCEPTIN® plus an AI, among HER2-positive and Hormone Receptor positive metastatic breast cancer patients, who had prior HERCEPTIN® based chemotherapy and endocrine therapy in the neo(adjuvant) and/or first line metastatic setting. This dual HER2 blockade combination offers an effective and safe chemotherapy-sparing alternative treatment regimen for this patient population. Phase III, Randomized Study of Dual Human Epidermal Growth Factor Receptor 2 (HER2) Blockade With Lapatinib Plus Trastuzumab in Combination With an Aromatase Inhibitor in Postmenopausal Women With HER2-Positive, Hormone Receptor–Positive Metastatic Breast Cancer: ALTERNATIVE. Johnston SR, Hegg R, Im S, et al. J Clin Oncol 2017;36:741-748