Glossary of terms

Short definition 

An aromatase inhibitor is a chemical that can potentially disrupt estrogen production by suppressing the activity of the aromatase enzyme, which is responsible for converting androgens into estrogens. While some natural substances produced by the body or consumed with food can have mild to moderate inhibitory effects, synthetic aromatase inhibitor (AI) drugs have a particularly potent impact on estrogen-related conditions, including gynecomastia in men and hormone receptor-positive (HR+) breast cancer in postmenopausal women. 

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Short definition 

A CDK4/6 inhibitor is a chemical that suppresses the activity of cell-cycle regulating enzymes, cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6). CDKN2A (p16^INK4a) and CDKN2B (p15^INK4b) are key enzymes that naturally inhibit CDK4 and CDK6 in the human body. In some health conditions, including certain types of cancer, these natural CDK4/6 inhibitors are downregulated or lost entirely. Their replacement with synthetic compounds, such as palbociclib, ribociclib, and abemaciclib, can potentially block the proliferation of cancer cells.¹ 

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Short definition 

CDK4/6 inhibitor drugs are synthetic compounds that block the activity of cell-cycle regulating enzymes, cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6), thereby preventing excessive cell proliferation. When the production or function of natural CDK4/6 inhibitors, such as p16 (INK4a) and p15 (INK4b), is compromised, these inhibitor drugs can serve as substitutes. They are primarily used in cancer therapy, particularly for treating hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR-positive, HER2-negative) breast cancer. 

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Short definition 

Endocrine therapy, commonly referred to as hormone therapy, is a medical treatment aimed at various health conditions, including certain cancers. It works by adjusting hormone levels or altering their activity within the body. This therapy employs diverse strategies, which may include adding or blocking specific hormones or completely removing hormone-producing glands. 

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Short definition 

Endocrine therapy for breast cancer is a primary medical treatment used in hormone receptor-positive breast cancer. It aims to reduce the body’s natural production of hormones, such as progesterone or estrogen, or block their effects entirely. This prevents cancer cells, otherwise stimulated by these hormones, from growing. 

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Short definition 

A natural aromatase inhibitor is a substance produced in the body or found in natural foods that can block the activity of the aromatase enzyme. By inhibiting aromatase, such natural substances can prevent the enzyme from catalyzing the reaction that produces the estrogen hormone. 

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