Neoadjuvant Lenvatinib Combined With Letrozole in Hormone Receptor Positive Breast Cancer

Hypothesis:

We hypothesize that combining a RET inhibitor such as lenvatinib with endocrine therapy may potentiate anti-tumor effects in ER+ breast cancers in the clinic. Given that RET inhibition is the primary mechanism of action of lenvatinib, we further hypothesize that RET expression in the breast tumor may be a biomarker that predicts for better response to the combination of a RET inhibitor and endocrine therapy in both a neoadjuvant (Part A) and a metastatic (Part B) setting.

Primary Objectives

• To confirm the dose of lenvatinib that can be safely combined with letrozole in the lead-in Phase Ib part of the study.
• Part A (For patients with non-metastatic breast cancer undergoing neoadjuvant treatment) : To determine the overall clinical response (measured by ultrasound) and pathological complete response rate after 2 weeks of neoadjuvant single agent lenvatinib followed by 12 weeks of letrozole combined with lenvatinib and compare with historical controls treated with single agent letrozole.
• Part B (For patients with metastatic breast cancer and who have tumor lesion that can be serially biopsied safely): to determine the clinical response (measured by RECIST criteria) after 2 weeks of single agent lenvatinib followed by continuous dual therapy of lenvatinib and letrozole, until time of progression or intolerability.

Secondary Objectives

• To evaluate the overall biological effects (Ki67 changes, histological response, apoptosis, RET and downstream targets such as AKT and ERK) of 2 weeks of single agent lenvatinib, and of letrozole + lenvatinib, in ER positive breast cancer, respectively.
• To identify biological predictors for treatment response to letrozole + lenvatinib in ER positive breast cancer using pharmacokinetics, pharmacogenetics, genomics and proteomics strategies.
• To compare the following parameters between RET positive versus RET negative, ER positive breast cancer:

• Part A :

i. Clinical response (measured by ultrasound) and biological effects of 2 weeks of single agent lenvatinib, ii. Clinical response (measured by ultrasound) and biological effects after 2 weeks of single agent lenvatinib followed by 12 weeks of letrozole combined with lenvatinib

-Part B : i. Clinical response measured by RECIST criteria after 2 weeks of single agent lenvatinib followed by letrozole combined with lenvatinib ii. Progression-free and overall survival with letrozole combined with lenvatinib

Inclusion criteria

• Female, age ≥ 18 years.
• Histologic or cytologic diagnosis of breast carcinoma.
• Part A: T1-4 breast cancer with measurable primary breast tumor, defined as palpable tumor with both diameters 2.0cm or greater as measured by caliper. Newly diagnosed metastatic patients with measurable primary breast tumor ≥2cm are eligible provided that there are plans for toilet mastectomy after completing 14 weeks of pre-operative drug therapy. Patients must not have received prior chemotherapy or hormonal therapy for the treatment of the current breast cancer.
• Part B: Patients with metastatic breast cancer with measurable tumor by RECIST criteria.Patients previously treated with letrozole are eligible if they progressed on letrozole ≥1 year after adjuvant treatment, or ≥ 6 months in the metastatic setting.
• ECOG 0-1.
• Estimated life expectancy of at least 12 weeks.
• Adequate organ function including the following:

• Bone marrow:
• Absolute neutrophil (segmented and bands) count (ANC) ≥ 1.5 x 109/L
• Platelets ≥ 100 x 109/L
• Hepatic:
• Bilirubin ≤ 1.5 x upper limit of normal (ULN),
• ALT or AST ≤ 2.5x ULN, (or ≤5 X with liver metastases)
• Renal:

Creatinine ≤ 1.5x ULN

• Post-menopausal women. Post-menopausal status is defined either by

• Age ≥ 60 years and one year or more of amenorrhea
• Age < 60 years and one year or more of amenorrhea (in the absence of ovarian suppression) and with estradiol and FSH levels consistent with menopause, *Treatment with a luteinizing hormone-releasing hormone (LHRH) agonist (goserelin acetate or leuprolide acetate) is not permitted for induction of ovarian suppression for Part A (patients with non-metastatic disease receiving the study treatment as neoadjuvant therapy).

However, in Part B (patients with metastatic disease), pre-menopausal women who are treated with medical ovarian suppression with post-menopausal levels of estradiol (institutional limits) at time of study entry and who will continue to be suppressed with 4-weekly LHRH agonist during study treatment may be enrolled. If these patients were previously on 12-weekly long-acting LHRH agonist, this has to be switched to 4-weekly LHRH agonist while the patient is on study treatment.

• Signed informed consent from patient or legal representative.

Exclusion criteria

• Treatment within the last 30 days with any investigational drug.
• Concurrent administration of any other tumor therapy, including cytotoxic chemotherapy, hormonal therapy, and immunotherapy.
• Major surgery within 28 days of study drug administration.
• Active infection that in the opinion of the investigator would compromise the patient's ability to tolerate therapy.
• Pregnancy.
• Breast feeding.
• Serious concomitant disorders that would compromise the safety of the patient or compromise the patient's ability to complete the study, at the discretion of the investigator.
• Active bleeding disorder or bleeding site.
• Non-healing wound.
• Poorly controlled diabetes mellitus.
• Second primary malignancy that is clinically detectable at the time of consideration for study enrollment.
• Symptomatic brain metastasis.
• History of significant neurological or mental disorder, including seizures or dementia.