CYTOPLASMIC CYCLIN E MEDIATES RESISTANCE TO AROMATASE INHIBITORS IN BREAST CANCER

Almost seventy percent of patients with breast cancer have tumors that express hormone receptors and need hormonal therapy. Aromatase inhibitors (AIs) block estrogen biosynthesis and are considered as the first line hormonal therapy for ER+ post-menopausal patients. However, resistance to these drugs remains a major challenge in clinic and the biology of such resistance is not completely understood. Cyclin E is deregulated in breast cancer through generation of low molecular weight isoforms that renders patients to a poor survival. Herein, we show that HR+ patients with LMW-E expressing tumors show diminished early response to neo-adjuvant AIs as well as poor recurrence-free survival. In addition, xenografts with LMW-E expression are unresponsive to letrozole. Using LMW-E inducible model system, we show that LMW-E expression bypasses cell cycle inhibition of AIs through up-regulation of CDK2, Rb, and phospho-Rb in a reversible manner. Lastly, we show that LMW-E expressing breast cancer cells respond to dinaciclib but not palbociclib. Taken together, this study suggests that targeting CDK2 by inhibitors such as dinaciclib in combination with AIs is a potential therapeutic strategy for HR+ postmenopausal breast cancer patients with LMW-E expressing tumors

Rapid Breast Cancer Disease Progression Following Cyclin Dependent Kinase 4 and 6 Inhibitor Discontinuation.

Background: CDK 4 and 6 inhibitors (CDK4/6i), which arrest unregulated cancer cell proliferation, show clinical efficacy in breast cancer. Unexpectedly, a patient treated on a CDK4/6i-based trial, as first-line therapy in metastatic breast cancer, developed rapid disease progression following discontinuation of study drug while receiving standard second-line therapy off trial. We thus sought to expand this observation within a population of patients treated similarly at The University of Texas MD Anderson Cancer Center. Methods: Using an IRB-approved protocol, 4 patients previously enrolled on CDK4/6i trials were analyzed for outcomes after discontinuing study drug. These patients were treated on a randomized trial of first-line endocrine therapy +/- a CDK4/6i. Rapid disease progression was defined as progression occurring within 4 months of CDK4/6i discontinuation. Results: In total, 4 patients developed rapid disease progression and died; 2 of whom died within 6 months of CDK4/6i discontinuation. Conclusion: This case series suggests a potential for rapid disease progression following CDK4/6i discontinuation. However, the clinical course following progression must be validated in large CDK4/6i clinical trials and standard-of-care cohorts. If confirmed, such observations may alter the algorithm for subsequent therapy in patients with disease progression on CDK4/6i. Nevertheless, the need remains to define a mechanistic basis for this rapid progression and formulate alternative therapeutic strategies

Rapid Breast Cancer Disease Progression Following Cyclin Dependent Kinase 4 and 6 Inhibitor Discontinuation.

Background: CDK 4 and 6 inhibitors (CDK4/6i), which arrest unregulated cancer cell proliferation, show clinical efficacy in breast cancer. Unexpectedly, a patient treated on a CDK4/6i-based trial, as first-line therapy in metastatic breast cancer, developed rapid disease progression following discontinuation of study drug while receiving standard second-line therapy off trial. We thus sought to expand this observation within a population of patients treated similarly at The University of Texas MD Anderson Cancer Center. Methods: Using an IRB-approved protocol, 4 patients previously enrolled on CDK4/6i trials were analyzed for outcomes after discontinuing study drug. These patients were treated on a randomized trial of first-line endocrine therapy +/- a CDK4/6i. Rapid disease progression was defined as progression occurring within 4 months of CDK4/6i discontinuation. Results: In total, 4 patients developed rapid disease progression and died; 2 of whom died within 6 months of CDK4/6i discontinuation. Conclusion: This case series suggests a potential for rapid disease progression following CDK4/6i discontinuation. However, the clinical course following progression must be validated in large CDK4/6i clinical trials and standard-of-care cohorts. If confirmed, such observations may alter the algorithm for subsequent therapy in patients with disease progression on CDK4/6i. Nevertheless, the need remains to define a mechanistic basis for this rapid progression and formulate alternative therapeutic strategies