Study on How HSD3B1 Gene Mutation Affects Treatment in Stage I-III Breast Cancer

Inclusion Criteria

• Must be a female aged 18 years or older.
• Must be postmenopausal, which can be confirmed by:
  • Being 60 years or older.
  • Being under 60 but having stopped regular periods for at least 12 months without other causes, or having hormone levels in the postmenopausal range.
  • Having had both ovaries removed.
• Must have a confirmed diagnosis of stage I-III breast cancer.
• Tumor must be at least 1.0 cm in size and enough tissue must remain after initial biopsy for further testing.
• Must be a candidate for surgery to remove the tumor.
• Cancer must be estrogen receptor-positive (ER+) with more than 1% positive cells.
• Cancer must have a Ki67 level of 10% or higher.
• Cancer must be HER2-negative.
• Must be willing to follow all study procedures and be available for the study duration.
• Previous use of hormone contraceptives or replacement therapy is allowed if stopped more than 6 months before diagnosis.
• Must be able to take oral medication and willing to follow the study treatment plan.

Exclusion Criteria

• Tumor biopsy sample is not likely to provide enough tissue for testing.
• Cancer is inoperable or has spread to other parts of the body.
• Have received any prior treatment for breast cancer, including radiation, surgery, or hormone therapy.
• Have had hormone therapy for breast cancer treatment or prevention within 1 year before joining the study.
• Plan to undergo chemotherapy before surgery.
• Used hormonal contraceptives within 6 months of diagnosis.
• Have taken another investigational drug or treatment within 28 days before starting letrozole.
• Have a history of allergic reactions to letrozole or similar medications.
• Have uncontrolled illnesses such as ongoing infections, heart failure, unstable chest pain, irregular heartbeats, or psychiatric conditions that would interfere with the study.