Description

Tamoxifen, often sold under the brand name Nolvadex, is a non-steroidal medication that belongs to a class of drugs called Selective Estrogen Receptor Modulators (SERMs). It is a type of hormonal therapy used primarily in the treatment and prevention of breast cancer. It can be administered as a tablet or liquid and is effective in both pre- and post-menopausal women, as well as men with breast cancer.

Indications

Tamoxifen is primarily indicated for the treatment and prevention of breast cancer, specifically in cases where the cancer is “estrogen receptor-positive” (ER+). Its key indications include:

• Treatment of Breast Cancer: It is used to treat both early-stage and advanced (metastatic) ER+ breast cancer in men and women.
• Adjuvant Therapy: As an add-on treatment after surgery and radiation therapy to reduce the risk of cancer recurrence.
• Risk Reduction: For women at high risk of developing breast cancer.
• Ductal Carcinoma In Situ (DCIS): To reduce the risk of developing invasive breast cancer in women who have had surgery and radiation for DCIS.

It also has some off-label uses, such as treating anovulatory infertility and gynecomastia.

Mechanism of Action

Tamoxifen’s mechanism of action is complex and is the reason it is categorized as a SERM. Its effect varies depending on the tissue it is acting on.

• Antagonistic Effect (Anti-Estrogenic): In breast tissue, tamoxifen acts as an estrogen receptor antagonist. It works by competitively binding to estrogen receptors on breast cancer cells. This prevents the body’s natural estrogen from binding to these receptors. Since many breast cancers are fueled by estrogen, blocking these receptors stops the growth signals that estrogen sends to the cancer cells, thereby inhibiting their proliferation.
• Agonistic Effect (Estrogenic): In other tissues, such as the uterus and bone, tamoxifen can act as a weak estrogen receptor agonist. This means it mimics the effects of estrogen, which can be both beneficial and harmful.
  • Beneficial: Its estrogenic effect on bone tissue helps to maintain bone density, which can be a positive side effect in postmenopausal women at risk of osteoporosis.
  • Harmful: The estrogenic effect on the uterine lining can increase the risk of developing endometrial changes, including hyperplasia, polyps, and in rare cases, uterine cancer.