Capecitabine in Metastatic Breast and GI Cancers

Inclusion Criteria: * Women with metastatic breast cancer OR men and women with metastatic gastrointestinal (GI) cancer * There is no limit to the number of prior chemotherapy or endocrine therapy regimens received. Use of a previous fluoropyrimidine-containing regimen in advanced / metastatic setting is permitted as long as the subject discontinued the regimen for reasons other than progression. * No restriction on the use of fluoropyrimidine-containing regimen in the neoadjuvant or adjuvant setting * For metastatic colorectal cancers, patients starting maintenance capecitabine after a course of oxaliplatin or irinotecan based chemotherapy are eligible. * Measurable or non-measurable disease per RECIST criteria 1.1 * Must have completed prior chemotherapy or radiation therapy at least 2 weeks prior to registration * Pathologic confirmation of respective malignancies. Biopsy of metastatic disease is preferred but not mandatory. * Performance Status: Eastern Cooperative Oncology Group (ECOG) Performance Score (PS) 0-2 * Adequate organ and marrow function as defined below: * Absolute neutrophil count ≥ 1,000/ microLiter (uL) * hemoglobin ≥ 7 g/L * platelets ≥ 50,000/uL * total bilirubin ≤ 2 X the Institutional Upper Limit of Normal (IULN) * o Aspartate Aminotransferase (AST) ( Serum Glutamic Oxaloacetic Transaminase \[SGOT\]) ≤ 5 X IULN * Alanine Aminotransferase (ALT) (Serum Pyruvic Glutamic Transaminase \[SPGT\]) ≤ 5 X IULN * creatinine clearance \> 50 milliliters per minute (ml/min) * Women of childbearing potential must agree to use adequate contraception. * Subjects may have previously treated brain or Central Nervous System (CNS) metastasis with radiation completed at least 2 weeks prior to registration. Prior radiation to places other than CNS disease must be completed at least 14 days prior to registration. Any number of prior radiation therapy regimens is allowed provided all toxicity of prior therapy is resolved to grade 1 or less. * Life expectancy of \>3 months Exclusion Criteria: * Patient has used Capecitabine in a past regimen for metastatic disease. * Patient is currently using, or planning to use another investigational agent. * Patient with known Dihydropyrimidine Dehydrogenase (DPD) deficiency * Patient has symptomatic brain or CNS metastases. * Patient has leptomeningeal disease * Patient is pregnant or nursing * Subjects must have no barriers to taking oral medications, for example uncontrolled nausea, vomiting, diarrhea at baseline, lack of physical integrity of the upper gastrointestinal tract, or malabsorption syndrome. * No recent (≤ 3months) of partial or complete bowel obstruction unless surgically corrected.