Breast cancer tissue estrogen levels on an average exceed plasma as well as benign breast tissue levels. To evaluate the contribution of intra-tumor aromatization to individual tumor estrogen levels (estradiol, E2; estrone, E1; estrone sulfate, E1S), breast cancer tissue sections obtained during mastectomy in 28 postmenopausal breast cancer patients were stained for aromatase protein expression using the aromatase antibody 677. The findings were correlated to intra-tumor estrogen levels determined with a highly sensitive HPLC-RIA. Staining with 677 alone (irrespective of the hormone receptor status) revealed no difference in tumor E2 levels comparing 677+ versus 677- tumors, although a non-significant trend towards higher tumor E1 and E1S levels was observed in 677+ breast cancers. In contrast, tumor levels of E(2) were significantly higher in ER+ tumors compared to ER- tumors (P<0.001) and to benign breast tissue from the same breast (P<0.001). Analysing the additional effect of positive staining with the aromatase antibody 677 on tumor estrogen levels in the subgroup of ER+ tumors, revealed significantly higher tumor levels of E2 (mean level of 544.7 versus 197.1 fmol/g tissue) as well as a non-significant trend concerning tumor E1 (mean level of 296.9 versus 102.1 fmol/g tissue). The mean tumor tissue E1S level was observed somewhat lower in ER+677+ (103.5 fmol/g) versus ER+677- tumors (190.1 fmol/g). In the subgroup of ER+PgR+ tumors, tissue levels of E2 were also found to be significantly higher among 677+ compared to 677- tumors: 873.2 fmol/g (95% CI 395.9-1925.6) versus 217.9 fmol/g (95% CI 88.8-534.9) (P=0.015). In conclusion, our results indicate a moderate effect of aromatase enzyme expression evaluated by IHC using the antibody 677 on intra-tumor estrogen levels among ER+ breast cancers. A substantial interindividual variation in the ratios between the individual estrogen fractions suggests additional effects, like alterations in other enzymes to be involved in the intra-tumor estrogen homeostasis.
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