Aromatase activity in primary and metastatic human breast cancer

Aromatase activity was measured in 104 primary and 24 metastatic breast cancer patients. The assay employed quantitates the production of ³H water release from 1β‐[³H] androstenedione after aromatization. Of 104 human primary breast tumors studied, 64 contained measurable aromatase activity, ranging from 5–70.5 pmol estrone formed/g protein/hour. In primary breast cancers there was no difference in levels of aromatase activity when analyzed by menstrual status or age by decade. Aromatase activity was similar in small and large primary tumors. The median aromatase activity of primary breast tumors (8.6 pmol/g/h) was similar to that found in metastatic breast cancer deposits (12.0 pmol/g/h). Aromatase activity did not correlate with either estrogen (ER) or progesterone (PR) receptor concentration in the tissues assayed. In this regard there were 33 ER⁻ PR⁻ tumor biopsies. Twelve of these 33 tumors contained aromatase activity greater than 10 pmol/g/hour. Cancer 59:779‐782, 1987.