capecitabine -- metabolic

http://www.medscape.com/viewarticle/712105

The study authors found that the addition of capecitabine seemed more effective in estrogen-receptor (ER)-positive than in ER-negative breast cancers, Dr. O'Regan points out.

"The positive findings in the capecitabine group could be explained by the fact that over three quarters of patients had ER-positive cancers," she writes. "There is currently no plausible mechanism to explain why capecitabine would be more effective in ER-positive disease, but this might warrant further study."

Capecitabine in advanced breast cancer: Predictive factors for response.

http://www.asco.org/ascov2/Meetings/Abstracts?&vmview=abst_detail_view&confID=55&abstractID=31750

The only positive correlation to predict response was ER positivity (p = 0.04).

http://www.ncbi.nlm.nih.gov/pubmed/18765464

Thymidine phosphorylase expression and benefit from capecitabine in patients with advanced breast cancer.