Fulvestrant Injection

• Type: Hormonal (endocrine) therapy for breast cancer

• Drug Class: Selective Estrogen Receptor Downregulator (SERD)

• Form: Intramuscular (IM) injection, typically given in the buttock (gluteal muscle)

How It Works

• Fulvestrant binds to estrogen receptors (ER) on breast cancer cells.

• It causes receptor degradation and completely blocks estrogen signaling.

• This leads to slowed growth or death of ER-positive breast cancer cells, which rely on estrogen for survival.

Common Uses

Fulvestrant injection is primarily used for:

• Hormone receptor-positive (HR+), HER2-negative advanced or metastatic breast cancer in postmenopausal women

• Often used after progression on other hormone therapies like tamoxifen or aromatase inhibitors

• Can be combined with CDK4/6 inhibitors (e.g., palbociclib, ribociclib) for improved outcomes in advanced disease

Advantages

• Pure estrogen receptor antagonist (no partial agonist activity, unlike tamoxifen)

• Monthly injection → convenient dosing schedule

• Useful in patients resistant to other hormone therapies

• Generally well tolerated compared to chemotherapy

Possible Side Effects

Common:

• Injection site pain or inflammation

• Hot flashes

• Mild nausea

• Fatigue

• Joint or muscle pain

Less Common but Important:

• Elevated liver enzymes

• Risk of bleeding (use caution in patients on anticoagulants)

• Rare allergic reactions

Precautions

• Should not be used in patients with severe liver disease without dose adjustment

• Not recommended during pregnancy or breastfeeding

• Monitor liver function tests during treatment

• Caution in patients with bleeding disorders or thrombocytopenia