Inclusion Criteria:

- Patients with measurable locally advanced or metastatic breast cancer who completed
124I PET/CT imaging study.

- Patients who are 18 years of age or older.

- Patients must have a life expectancy of at least 3 months.

- I 124 dosimetry completed with thyroid dose to 500 cGy or less and tumor dose of 2500
cGy or more.

- I131 therapeutic dose calculated from dosimetry. Dose must be in a range of 25 to 150
mCi.

- Patients with Eastern Cooperative Oncology Group (ECOG) Performance Status 0-3 will
be eligible.

- Use of concurrent systemic therapy (hormonal or cytotoxic) if associated with stable
disease for at least three months prior to treatment.

- Women with locally advanced breast cancer and simultaneous metastases, even if
surgery to eradicate local disease has taken place.

- Thyroid stimulating hormone (TSH) must be < 0.4 uIU/mL.

- White blood cell count >= 1,500 and platelet count >= 40,000

- Women receiving thyroid hormone supplements and methimazole.

- Ability to understand and the willingness to sign a written informed consent
document.

- Premenopausal women must use contraception while receiving this treatment and during
follow-up period of 42 days.

Exclusion Criteria:

- Stage 0-II breast cancer.

- Pregnant or nursing women.

- Not able to sign informed consent.

- Untreated psychiatric disorder.

- Women who have not had I124 PET/CT scan and dosimetry calculations.

- Radioiodide uptake in non-target organs or bone marrow does not exceed 25 cGy by
pre-treatment dosimetry.

- Received chemotherapy less than 4 weeks before.

- History of thyroid cancer.