What are the side effects of Fulvestrant (Faslodex)?

Side Effects of Fulvestrant (Faslodex)

The most common side effects of Fulvestrant include arthralgia (joint pain), hot flashes, nausea, fatigue, and injection site reactions, with most adverse events being mild to moderate in severity. 1

Common Side Effects

• Musculoskeletal effects: Arthralgia (joint pain) affects approximately 17% of patients, making it one of the most frequently reported side effects 1
• Vasomotor symptoms: Hot flashes occur in approximately 11% of patients 1, 2
• Gastrointestinal disturbances:
  • Nausea 2, 3
  • Vomiting 2
  • Diarrhea 2
• Injection site reactions: Due to its intramuscular administration route 3, 4
• Constitutional symptoms:
  • Fatigue/asthenia 2
  • Headache 2

Comparison with Other Endocrine Therapies

• Fulvestrant has a more favorable joint disorder profile compared to aromatase inhibitors like anastrozole 5
• The quality of life outcomes with fulvestrant are similar to those with anastrozole 1
• Unlike tamoxifen, fulvestrant has no known estrogen agonist effects, which may result in a different side effect profile 2, 6

Severe Side Effects

When used in combination therapy with CDK4/6 inhibitors (common in current practice), additional side effects may occur:

• Hematologic toxicities:

  • With palbociclib: Grade 3-4 neutropenia (62% vs 0.6% with fulvestrant alone), leukopenia (25.2% vs 0.6%) 1
  • With abemaciclib: Grade 3-4 neutropenia (26.5% vs 1.7% with fulvestrant alone) 1
  • With ribociclib: Grade 3-4 neutropenia (46.6% vs 0% with fulvestrant alone) 1

• Gastrointestinal toxicities:

  • With abemaciclib: Diarrhea (86.4% all grades, 13.4% grade 3-4) 1

Special Considerations

• Febrile neutropenia rates are relatively low (0.6%) even when fulvestrant is combined with CDK4/6 inhibitors 1
• Serious adverse events directly attributed to fulvestrant alone are uncommon 2, 4
• Unlike some other hormonal therapies, fulvestrant is not associated with clinically significant effects on endometrial thickening, bone turnover markers, or sex hormone levels 5

Administration-Related Considerations

• Fulvestrant is administered as a monthly intramuscular injection (500 mg), sometimes with a loading dose regimen (500 mg every 2 weeks for 3 doses, then monthly) 1
• The higher dose regimen (500 mg) has shown improved efficacy over the lower dose (250 mg) without additional toxicity 1, 5

Impact on Quality of Life

• When used as monotherapy, fulvestrant generally maintains quality of life 1
• When combined with CDK4/6 inhibitors like palbociclib, patients may experience:
  • Maintained global quality of life 1
  • Improved emotional functioning 1
  • Improved pain control 1
  • Delayed deterioration in physical and social functioning 1

The side effect profile of fulvestrant makes it a well-tolerated option for hormone receptor-positive metastatic breast cancer in postmenopausal women, particularly those who have progressed on prior endocrine therapy 5, 2.