Relevance of cell kinetics to hormonal response of receptor-positive advanced breast cancer

Summary The relationship between cell kinetics and hormonal status and the relevance of the cell kinetic variable on success of hormonetherapy in estrogen receptor positive (ER+) breast tumors were analyzed in patients with advanced disease. Cell kinetics were evaluated as in vitro³H-thymidine labeling index (LI), and estrogen receptor (ER) and progesterone receptor (PgR) with the dextran-coated charcoal technique. The analyses performed on primary tumor or soft tissue metastases from 52 patients showed a general association between the presence of hormone receptors and low proliferative activity, or the absence of receptors and high proliferative activity (ER and L.I.: p>0.05; PgR and L.I.: p = 0.05). However, hormonal status and cell kinetic status were unrelated in about 40% of the cases. Clinical response to additive hormonotherapy was analyzed in relation to pretreatment LI in 29 patients with ER+ tumors. Time to reach maximum response was significantly longer in slow than in fast proliferating tumors, but complete remission was reached in 88% of slow proliferating tumors compared to only 46% of fast proliferating tumors. These preliminary results show that ER+ fast proliferating tumors largely escape hormonal control, and if confirmed on larger series, could identify cell kinetics as an important tool to select patients who will benefit from hormonal treatment.