A Clinical Trial Evaluating the Safety and Clinical Activity of Radioiodide (131I-) as a Novel Targeted Therapy for Metastatic Breast Cancer That Overexpresses Functional Na/I Symporter

The primary objectives of the study are as follows: 1. To evaluate the feasibility of using 124I- PET/CT scans to identify patients whose metastatic lesions accumulate radioactive iodide and therefore are candidates for 131I- therapy. 2. Determine the frequency of iodide (124I) enriching metastatic breast cancer. 3. Evaluate the safety and clinical activity of one-time 131I treatment to patients who screen positive on 124I- PET/CT screening, positivity is defined as calculated iodide enrichment that will allow delivering 2000 cGy or more radiation to one or more metastatic lesion by administering up to 200mCi 131I-. The secondary objectives of the study are as follows: 1\. To investigate a correlation between NIS expression in tumor tissue with 124I- uptake on screening PET/CT scan The Phase I portion will follow a 3+3 design with 4 dose levels (30, 60, 120, and 200 mCi) of I- treatment. The maximum tolerated dose will be used in the Phase II efficacy assessment which will follow a Simon's optimal two-stage design. The primary efficacy measure is objective tumor response rate (CR or PR) with targeted activity level of \> 20% response rate. The study will be terminated for futility if no tumor response is seen in the first 12 patients. If futility criteria is not met, a total of 37 eligible patients will be enrolled in the Phase II portion. If 4 or more responses are seen after 37 patients were evaluated, then the investigators will conclude that the regimen warrants further study.