Chemotherapy

Drugs such as cyclophosphamide, ifosfamide, or busulfan may harm eggs or trigger early menopause.

Radiation Therapy

Pelvic, abdominal, or brain radiation can damage ovaries, uterus, or hormones that regulate ovulation.

Surgery

Removal of ovaries or uterus causes permanent infertility; pelvic surgery may affect blood flow or hormone signals.

Hormone or Targeted Therapy

Drugs that block estrogen (tamoxifen, aromatase inhibitors) can temporarily suppress fertility.

Stem-Cell or Bone-Marrow Transplant

Usually involves very high chemo or radiation doses that can permanently stop egg production.