INFLUENCE OF LOBULAR DEVELOPMENT ON BREAST EPITHELIAL-CELL PROLIFERATION AND STEROID-HORMONE RECEPTOR CONTENT

The development of the breast evolves through progressive formation of lobular structures. Lobules type 1 (Lob 1) are the most undifferentia ted ones; they evolve to lobules type 2 (Lob 2), and those to type 3 ( Lob 3), in response to mainly ovarian hormones. Although estradiol and progesterone act by binding to their specific receptors, their conten t in these structures and how they correlate with proliferative activi ty are not known. Normal breast tissues obtained from 40 reduction mam moplasties performed for cosmetic reasons in women free of mammary pat hology were processed for light microscopy. Paraffin sections were imm unoreacted with antibodies against estrogen receptor (ER), progesteron e receptor (PgR), and proliferating cell nuclear antigen (PCNA). The n umber of cells positively labeled with each one of the three antibodie s was quantitated in Lob 1, 2 and 3, and expressed as a percentage of the total number of cells. ER were positive in Lob 1 (21%) and Lob 2 ( 10%), but negative in Lob 3. PgR were positive in Lob 1 (66%) and 2 (6 8%), decreasing in Lob 3 (31%). The highest percentage of PCNA positiv e cells were found in Lob 1 (40%), decreasing in Lob 2 (33%) and Lob 3 (11%). These results indicate that the normal breast epithelium conta ins ER and PgR, but the former is at higher levels in Lob 1, which als o expresses greater proliferative activity as demonstrated with PCNA.