Provided herein are methods of determining tumoral sensitivity to hormonal (endocrine) therapy based upon an index of estrogen receptor (ER)- and progesterone receptor (PR)-related genes, referred to as the sensitivity to endocrine therapy index (SETER/PR index), and may have additional consideration for the proportion of ER gene (ESRI) RNA transcripts that contain a mutation relative to the value of the SETER/PR index. Further provided are methods of treating breast cancer patients determined to be sensitive to an endocrine therapy by the SETER/PR index.