RATIONALE: Estrogen can stimulate the growth of breast cancer cells. Hormone therapy using tamoxifen may fight breast cancer by reducing the production of estrogen. It is not yet known if prolonged tamoxifen is more effective than shorter tamoxifen therapy following curative treatment for breast cancer.

PURPOSE: This randomized phase III trial is studying giving tamoxifen over a prolonged period of time to see how well it works compared to giving tamoxifen over a shorter period of time in treating patients who have had a breast tumor removed.

OBJECTIVES:

• Assess the balance of risks and benefits in prolonging the duration of adjuvant tamoxifen by at least 5 years in patients with curatively treated breast cancer who have already had about 5 years of adjuvant tamoxifen.

OUTLINE: This is a randomized study. After about 5 years of adjuvant tamoxifen, recurrence-free patients are randomized to stop tamoxifen treatment immediately or to continue tamoxifen treatment for at least 5 more years.

Patients are followed annually.

PROJECTED ACCRUAL: Approximately 20,000 patients will be accrued for this study.

DISEASE CHARACTERISTICS:

• Curatively treated carcinoma of the breast

• Currently taking adjuvant tamoxifen

  • Must be substantial uncertainty as to whether or not to continue tamoxifen (i.e., no clear indication or definite contraindication to further treatment with tamoxifen)

PATIENT CHARACTERISTICS:

Age:

• Any age

Performance status:

• Not specified

Life expectancy:

• Not specified

Hematopoietic:

• Not specified

Hepatic:

• Not specified

Renal:

• Not specified

Other:

• Not pregnant or nursing
• No contraindications to receiving tamoxifen
• No other serious medical problems

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Prior biologic therapy allowed

Chemotherapy:

• Prior chemotherapy allowed

Endocrine therapy:

• See Disease Characteristics

Radiotherapy:

• Prior radiotherapy allowed

Surgery:

• Prior surgery allowed