TUKYSA® Combination in HER2-Positive Metastatic Breast Cancer Patients with Brain Metastases

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 290,560 new cases of breast cancer will be diagnosed in 2022 and about 43,780 individuals will die of the disease, largely due to metastatic recurrence.

The HER or erbB family of receptors consist of HER1, 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. 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), KADCYLA® (ado-Trastuzumab emtansine), ENHERTU® (Trastuzumab deruxtecan) and MARGENZA® (Margetuximab). 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 (OS). The superior benefit with dual HER2 blockade has been attributed to differing mechanisms of action and synergistic interaction between HER2 targeted therapies. Patients progressing on Dual HER2 blockade often receive KADCYLA® which results in an Objective Response Rate (ORR) of 44% and a median PFS of 9.6 months, when administered after HERCEPTIN® and a taxane. There is however no standard treatment option for this patient population following progression on KADCYLA®.

With advances in systemic therapies for this patient population, the incidence of brain metastases as a sanctuary site has increased. Approximately 50% of patients with HER2-positive metastatic breast cancer develop brain metastases. However, systemic HER2-targeted agents, including Tyrosine Kinase Inhibitors, as well as chemotherapy have limited antitumor activity in the brain. Local therapeutic interventions for brain metastases include neurosurgical resection and Stereotactic or Whole-Brain Radiation Therapy. There is a high unmet need for systemic treatment options to treat established brain metastases and reduce the risk for progression in the Central Nervous System (CNS).

TUKYSA® (Tucatinib) is an oral Tyrosine Kinase Inhibitor that is highly selective for the kinase domain of HER2 with minimal inhibition of Epidermal Growth Factor Receptor. In a Phase 1b dose-escalation trial, TUKYSA® in combination with HERCEPTIN® and XELODA® (Capecitabine) showed encouraging antitumor activity in patients with HER2-positive metastatic breast cancer, including those with brain metastases.

HER2CLIMB is an international, randomized, double-blind, placebo-controlled trial in which the combination of TUKYSA® plus HERCEPTIN® and XELODA® was compared with placebo plus HERCEPTIN® and XELODA®. A total of 612 patients with unresectable locally advanced or metastatic HER2-positive breast cancer, who were previously treated with HERCEPTIN®, PERJETA® (Pertuzumab) and KADCYLA® (ado-Trastuzumab emtansine) were enrolled. Patients were randomly assigned in a 2:1 ratio to receive either TUKYSA® 300 mg orally twice daily throughout the treatment period (N=410) or placebo orally twice daily (N=201), in combination with HERCEPTIN® 6 mg/kg IV once every 21 days, following an initial loading dose of 8 mg/kg, and XELODA® 1000 mg/m2 orally twice daily on days 1 to 14 of each 21-day cycle. Stratification factors included presence or absence of brain metastases, ECOG Performance Status and geographic region. The median patient age was 52 years and patient demographics as well as disease characteristics at baseline were well balanced between the two treatment groups. In the total treatment population, 47.5% had brain metastases at baseline, 48.3% in the TUKYSA® combination group and 46% in the placebo combination group. The Primary endpoint was Progression Free Survival (PFS). Secondary end points included Overall Survival (OS), PFS among patients with brain metastases, confirmed Objective Response Rate (ORR), and Safety.

At median follow-up of 29.6 months, median OS in all patients with brain metastases at baseline was 9.1 months longer in the TUKYSA® combination group compared to the placebo combination group (21.6 versus 12.5 months, HR=0.60; P<0.001), with a 40% reduction in the risk of death with the TUKYSA® combination. The estimated 1-year OS was 70.0% for the TUKYSA® combination group and 50.6% for the placebo combination group and the estimated 2-year OS was 48.5% and 25.1% respectively.

The researchers in this exploratory subgroup analyses reported efficacy outcomes for patients with brain metastases, as well as time to new brain lesion(s) as the site of first progression or death, in all patients enrolled in HER2CLIMB trial, at a median follow up of 29.6 months.

There was greater CNS Progression Free Survival in the TUKYSA® combination group compared with the placebo combination group and was 5.7 months longer (9.9 versus 4.2 months, HR=0.39; P<0.001), with a 61% reduction in the risk of CNS progression with the TUKYSA® combination. The estimated 1 and 2-year CNS Progression Free Survivals were 38.4% versus 7.9% and 19.3% versus 0%, respectively.

Among those with active brain metastases and measurable disease at baseline, the intracranial Objective Response Rates for the TUKYSA® combination group were 47.3% versus 20.0% for the placebo combination group, with a median duration of intra cranial response of 8.6 versus 3.0 months, respectively.

The risk of developing new brain lesions as the site of first progression or death was reduced by 45% in the TUKYSA® combination group versus the placebo-combination group (HR=0.55; P =0.006).

The authors concluded that in this exploratory subgroup analysis, TUKYSA® in combination with HERCEPTIN® and XELODA® provided a clinically meaningful survival benefit, while reducing the risk of developing new brain lesions. The authors added that HER2CLIMB is currently the only double-blind, randomized, controlled clinical trial for patients with HER2-positive metastatic breast cancer, that prospectively included patients with both active and stable brain metastases.

Tucatinib vs Placebo, Both in Combination with Trastuzumab and Capecitabine, for Previously Treated ERBB2 (HER2)-Positive Metastatic Breast Cancer in Patients With Brain Metastases: Updated Exploratory Analysis of the HER2CLIMB Randomized Clinical Trial. Lin NU, Murthy RK, Abramson V, et al. JAMA Oncol. Published online December 1, 2022. doi:10.1001/jamaoncol.2022.5610