These findings are in agreement with the hypothesis that AR may stimulate or inhibit breast cancer growth depending on ER status, AR transactivation, and the endocrine-metabolic environment of breast tumors.
Furthermore, gene encoding coagulation factor VII (F7) demonstrated the closest expression pattern with AR (CC=0.716) in the dataset and factor VII protein expression was significantly associated to that of AR in a cohort of 209 breast tumors.
In addition, C1orf64 closely correlated with AR expression in primary and metastatic breast tumors and C1orf64 expression was relatively higher in breast tumors with a lower grade and lobular histology.
Re-evaluation of the breast tumor immunohistochemistry has shown positive androgen receptor expression and negative expression for estrogen, progesterone and HER-2 receptors.
A majority (~70%) of breast tumors are found to express estrogen receptor, and a significant portion (~90%) of ER-positive (ER<sup>+</sup>) breast tumors are also androgen receptor-positive (AR<sup>+</sup>).
Eligible studies were identified by systematic review of electronic databases using the MeSH-terms "breast neoplasm" and "androgen receptor" and were selected after a qualitative assessment based on the REMARK criteria.
It has also been documented that AR is expressed in more than 60% of breast tumors, which promotes the growth of estrogen receptor-negative (ER<sup>-</sup>)/AR-positive (AR<sup>+</sup>) breast cancer cells.
To get more insight into the role of AR in breast cancer, we additionally performed a retrospective pooled analysis to determine the prognostic value of the AR using mRNA profiles of 7270 primary breast tumors.
Recent advances in the molecular classification of breast tumours have uncovered a subset of breast tumours associated with high expression of androgen receptor mRNA including the so-called 'luminal androgen receptor (LAR) tumours' and 'molecular apocrine tumours' (MATs).