A Proposed Model for the Prediction of Response to Endocrine Therapy in Breast Cancer from the Estrogen Receptor Status of One Site and the Number of Metastatic Sites

A mathematical model for prediction of response to endocrine therapy of breast cancer has been developed based on a clonal concept of metastatic spread. The model includes an expression of the likelihood of response of an estrogen receptor-positive site and an expression of the concordance of receptor assays when multiple sites are assayed. Both of these are raised to a power function based on the number of sites of metastases to yield a predicted response rate. An excellent fit of the predictions of this mathematical model and response data from a series of patients receiving endocrine therapy was observed. This model provides a worthwhile insight into the biology of response to endocrine therapy. The model may be extended and refined through additional analyses.