STAT5B and breast carcinoma: Work from our laboratory used selective overexpression of either Stat5a or Stat5b in the ER-positive MCF-7 human breast cancer cell line in vitro followed by PRL exposure to explore differences in Stat5a and Stat5b regulated transcripts on the Affymetrix platform, but this study also failed to confirm any of the modulated transcripts by qRT-PCR or validate the data in vivo[17].