Genistein in Preventing Breast Cancer in Women at High Risk for Breast Cancer

Inclusion Criteria:

* No known soy intolerance
* At increased risk of developing breast cancer in \>= 1 previously unaffected breast, as defined by any of the following:

  * Estimated 5-year risk of developing breast cancer using the Gail model, as defined by 1 of the following:

    * Gail score \>= 1.66%
    * Gail score \>= 0.1% for women age 20-29 years
    * Gail score \>= 1.0% for women age 30-39 years
  * Estimated 5-year risk of developing breast cancer using the Claus model:

    * Claus score \>= 1.66%
    * Claus score \>= 0.1% for women age 20-29 years
    * Claus score \>= 1.0% for women age 30-39 years
  * Prior diagnosis of unilateral in situ or invasive breast cancer OR history of atypical hyperplasia, BRCA 1 and/or BRCA 2 positivity
  * History of lobular carcinoma in situ
* No evidence of breast cancer, as determined by a negative mammogram within the past 6 months and a history and physical
* No previously diagnosed breast cancer unless all systemic therapy (including endocrine therapy) was completed at least 1 year ago
* Pre- or postmenopausal
* ECOG performance status 0-1
* Hemoglobin \> 10.0 g/dL
* Platelet count \> 100,000/mm\^3
* Absolute neutrophil count \> 1,000/mm\^3
* Creatinine \< 2.0 mg/dL
* SGPT \< 82 U/L
* SGOT \< 68 U/L
* Bilirubin \< 3 mg/dL\* \[Note: \* Patients with a higher level of bilirubin due to a familial metabolism may be eligible at the discretion of the investigator\]
* Life expectancy \> 2 years
* Not pregnant or nursing
* Negative pregnancy test
* Fertile patients must use effective barrier contraception
* Must be willing to keep a dietary diary
* No venous thrombosis within the past year
* No unrecognized or poorly controlled thyroid disease
* No other cancer within the past 5 years except nonmelanomatous skin cancer or noninvasive cervical cancer
* No other medical condition that, in the opinion of the investigator, would jeopardize either the patient or the integrity of the data obtained
* None of the following for \>= 2 weeks before the first random fine needle aspiration and during study participation:

  * Oral contraceptives
  * Soy supplements
  * High soy-containing foods
  * Fish oil supplements
  * Multivitamins
  * Vitamins C and E
  * Daily aspirin or nonsteroidal
  * Anti-inflammatory drugs
* No other concurrent investigational agents
* No concurrent warfarin or other blood thinners
* Female patient

Exclusion Criteria:

Women previously diagnosed with breast cancer will not be eligible unless all systemic therapy (including endocrine therapy) was completed at least one year previously

* Currently pregnant, or planning to become pregnant during the study period
* History of venous thrombosis within past year
* Medical conditions, which, in the opinion of the investigators would jeopardize either the patient or the integrity of the data obtained
* History of other cancer within the past five years, excluding non-melanomatous skin cancer, and non-invasive cervical cancer
* Known soy intolerance
* Unrecognized or uncontrolled thyroid disease, subjects may be on synthroid, but thyroid function must be in normal range or the patient's physician must document that the patient's thyroid is controlled.
* Currently receiving any other investigational agents
* Currently on coumadin, or other blood thinners
* History of breast augmentation implants.
* Rusults from patients who have \<4000 epithelial cells in either the first or the second random Fine-needle aspiration (rFNA) will not be included in the study.