Androgen receptor determination in breast cancer: a comparison of the dextran-coated charcoal method and quantitative...

Androgen receptor (AR) expression is prognostic for breast cancer. Techniques to determine AR levels include the dextran-coated charcoal method (charc-AR), which measures AR levels in both normal and cancer cells; immunohistochemical analysis (1HC-AR) of whole sections (WS), which targets cancer cells but relies on subjective assay interpretation; and IHC of tissue microarray (TMA) samples, an approach that can be inaccurate when AR heterogeneity is present. This study compared charc-AR (n=151) with quantitative IHC analysis (n=138) of WS and TMA samples (1.7 mm cylinder samples; 2.3 mm). Charc-AR results correlated poorly with IHC-WS and IHC-TMA results due to the presence of AR-positive noncancer cells. IHC-WS revealed intertumor and intratumor AR heterogeneity. Consequently, the IHC-WS and IHC-TMA results were similar for tumors in which the percentage of AR-positive WS samples was >80% (31% of tumors), but differed in other tumors due to TMA false negatives (33%). Computer simulation was used to determine the optimal number and size of TMA samples for reliable results, and showed that five to eight 1.7 mm samples, or up to sixty-four 0.6 mm samples, were needed for reliable AR determination for most tumors. Thus, AR determination by charc-AR is inaccurate due to evaluation of both normal and cancer cells. IHC is more sensitive and specific than charc-AR in WS samples, but not when applied to single or a few TMA samples.