Interrelationship between Estradiol and Tamoxifen Responses for Clinical Breast Carcinoma Cells Cultured on Contact-sensitive Plates

An in vitro assay system for predicting the estradiol (E₂) sensitivity of clinical cancer cells was applied to 54 patients with breast carcinoma to compare the responses to E₂ and tamoxifen (TAM) with the estrogen receptor (ER) status. We found that 18 of the 35 cases in the ER-positive group and 6 of the 19 cases in the ER-negative group were stimulated by E₂. It is suggested that ER status alone can not predict the response of cultured cells to E₂ in clinical breast cancer. Cell growth of 11/35 (31%) of the ER-positive cases and that of 8/19 (42%) of the ER-negative cases was inhibited by E₂. Since the cases inhibited by E₂ could not be distinguished by ER status alone, an assay system based on a quantitative proliferative response was considered necessary. There were 20 (83%) cases of inhibition by TAM among the 24 stimulated by E₂. Only 18/35 (51%) of the ER-positive group exhibited growth inhibition by TAM. In our (CSP) assay, 20 (83%) of the 24 cases stimulated by E₂ were inhibited by TAM, 10 (91%) of the 11 E₂-insensitive cases were insensitive to TAM and 13 (68%) of the 19 cases inhibited by E₂ were stimulated by TAM. In short, TAM response and E₂ response tended to be inversely related (43/54=80%, P <0.01). Furthermore, the E₂-response rate showed a good correlation with the TAM-response rate (R₂= 0.825). These results indicate the feasibility of predicting individual tumor responses to either E₂ or TAM by using CSPs.