Morphological detection of cell kinetics and progesterone receptor expression during growth and regression of pregnancy-dependent mammary tumors of GRS/A mice

Cell kinetics (cell proliferation and cell death) and the expression of progesterone receptor (PgR) during growth and regression of pregnancy-dependent mammary tumors (PDMT) of female GRS/A mice were investigated on the histologic level. Cell proliferation was determined using monoclonal anti-proliferating cell nuclear antigen (PCNA) antibody (PC10) and cell death was detected using the TUNEL method. PgR expression was determined using monoclonal anti-PgR antibody (10A9). In growing PDMT (type P tumor) obtained during days 16–20 of pregnancy, numerous PCNA labeling was observed in both the epithelial and mesenchymal cells, whereas PgR was found only in epithelial cells and no TUNEL signal was detected. In regressing PDMT obtained during days 0–5 of lactation, the level of PCNA labeling was low and the PgR-positive cells were preferentially labeled by the TUNEL staining, which led to microcyst formation (cystic degeneration). Pale cell carcinoma was shown to be pregnancy-dependent, since the tumor cells were universally PgR-positive, and TUNEL-positive signal with low PCNA-labeling was detected after the delivery.