Tamoxifen Citrate in Treating Patients With Metastatic or Recurrent Breast Cancer

OBJECTIVES: Primary * To correlate CYP2D6 (Cytochrome P450 2D6) score (0 vs 1-2) and progression-free survival (PFS) Secondary * To correlate CYP2D6 score (0 vs 1 vs 2) and PFS * To correlate CYP2D6 score (0 vs 1-2) and the proportion of these patients who are progression-free at 6 months. * To correlate endoxifen concentration with response * To correlate CYP2D6 with response * To correlate the presence of candidate estrogen receptor (ESR) 1 and 2 variant alleles, UDP-glucuronosyltransferases (UGT) 7, sulfotransferases (SULT) 1A1, other candidate genes and biomarkers to PFS and other tamoxifen related outcomes OUTLINE: This is a multicenter study. Patients receive oral tamoxifen citrate once daily on days 1-28. Treatment repeats every 28 days in the absence of disease progression or unacceptable toxicities. Blood, plasma, and tissue samples are collected periodically for laboratory studies. After completion of study therapy, patients are followed up every 3-6 months for 5 years.