The neoadjuvant setting has been the target of increasing interest recently, as it offers the possibility of direct evaluation of treatment effect on tumour size, better surgical results as well as for the possible research opportunities it provides via the comparative analysis of tumour biology and clinical outcomes before and after treatment.
Invasive lobular breast cancer (ILBC) is the second most common histologic subtype (5-15%) after invasive ductal breast cancer (IDBC). Despite clinical and pathologic differences, ILBC is still treated as IDBC. Indeed, subjects with ILBC tend to have lower response rates to conventional chemotherapeutic agents and some results have suggested that they might derive increased benefit with aromatase inhibitors.
CDK4/6 inhibitors in combination with endocrine therapy are FDA-approved for the treatment of ER-positive/HER2-negative metastatic breast cancer following the results of 7 positive phase 3 trials. These agents are currently tested in phase 3 studies in the adjuvant setting and might achieve the status of standard of care for subjects with ER-positive/HER2-negative early breast cancer treated with curative intent. In the NeoPAL (UCBG10/4, NCT02400567) neoadjuvant randomized study, Residual Cancer Burden (RCB) 0-1 status was achieved for 7.7% of subjects in the letrozole + palbociclib arm. This rate is not available for the 7 subjects with lobular breast cancer enrolled in this arm.
In lobular breast cancer, loss of E-cadherin (CDH1) expression is the most frequent oncogenic event and is present in 90% of cases. In vitro, ex vivo, and in vivo model systems as well as different functional profiling modalities (genetic and chemical screens) have been used to identify CDH1 synthetic lethality interactions. In vivo, ROS1 inhibitors produced profound antitumor effects in multiple models of E-cadherin-defective breast cancer, providing the preclinical rationale for assessing ROS1 inhibitors in this setting. A study is currently investigating this hypothesis in ER+/HER2- metastatic lobular breast cancer (NCT03620643).
Entrectinib is a potent small-molecule tyrosine kinase inhibitor that targets oncogenic rearrangements in NTRK, ROS1, and ALK. In vitro, entrectinib potently ROS1 at low nanomolar concentrations, with an average median inhibitory concentration of 0.007 μM against ROS1.
This single arm, multi-center, phase 2 trial will include pre and post-menopausal women with ER-positive/HER2-negative early stage invasive lobular carcinoma of the breast to evaluate the effect of combining endocrine therapy with entrectinib. Subjects will receive four 28-day cycles of letrozole 2.5 mg daily in combination with entrectinib 600 mg daily. Pre-menopausal women will receive goserelin 3.6 mg every 28 days.
Subjects' response to therapy will be evaluated at screening, after 2 cycles and after the 4 cycles of treatment by breast magnetic resonance imaging (MRI). An ECG will be performed at screening and then before cycle 2. Surgery will take place after at least 16 weeks of treatment, during week 18 (+ 7-day window). Breast and axillary surgery will follow local practice.
Post-operative therapy will be at the discretion of the investigator and will follow local practice.
