Extracellular proteins in breast tumor cytosol

Several proteins have been quantitated in cytosols prepared from benign and malignant tumors of the breast; orosomucoid, albumin, transferrin, complement 4, C-reactive protein alpha 2-macroglobulin and hemoglobin. With the exception of hemoglobin, concentrations of the proteins measured were significantly intercorrelated. Their relative abundance was close to that reported in blood, except for alpha 2-macroglobulin and hemoglobin which were present in lower amounts. From hemoglobin measurements it can be concluded that blood contamination contributed less than 10% to the cytosol proteins measured. When compared to albumin, none of the proteins investigated occurred in concentrations sufficient to indicate local synthesis of a magnitude that would significantly influence tumor environment. From the present data it can be concluded that extracellular proteins constitute about 50% of total cytosol protein. This indicates an exceptional capillary leakage in breast tumors possibly related to abnormal hormonal influences. There were, however, large individual variations and about 10% of the cytosols could be predicted to contain negligible amounts of cell-derived protein. There was a highly significant difference between benign and malignant tumors in their cytosol content of extracellular protein, benign tumors containing nearly twice as much albumin. It is suggested that measurement of an extracellular protein (albumin) should be included in tumor characterization to correct for cellularity and representativity of tumor samples used for steroid receptor determinations and for measurements of other parameters using "cytosol" protein to express specific activity.