What is the value of measuring MTA-1s in breast cancer?

The presence or absence of estrogen receptor (ER) expression in tumor cells affects prognosis and guides treatment choices. Kumar et al. suggest that a shortened form of the metastatic tumor antigen 1 (MTA1s) acts to sequester the estrogen receptor (ER) in the cytoplasm, inhibiting its ability to transactivate specific genes and, presumably, adding to the ER's ability to transduce non-genomic (cytoplasmic) signaling mechanisms. However, if the cancer is negative for ERalpha in the nucleus, but is positive for ERalpha in the cytoplasm, how does this sequestration affect the treatment of the patient or our understanding of the disease process? Cheng et al. caution that these results must be interpreted carefully with regard to what is known about estrogen-dependent and -independent tumor growth and chemotherapeutic strategies to destroy them.