A-B) Representative patient tumor responses to paclitaxel. Yellow arrows indicate tumors. A) Progression of a hormone receptor-positive liver metastasis. B) Marked improvement of a mediastinal lymph node. C) Waterfall plot showing treatment response to taxane therapy in a cohort of 37 metastatic breast cancer patients treated with singleagent taxane. Color indicates breast cancer receptor subtype; hormone receptor positive (HR+), triple negative (triple neg), or human epithelial growth factor receptor 2 positive (HER2+). D) Representative FISH images showing probes for centromeres 3, 7, and 9. The average percent non-modal chromosomes was used as a measure of chromosomal instability. E-F) Correlation of pre-treatment chromosomal instability with response to taxane treatment. Response cutoff was determined by RECIST 1.1 criteria (26), and is indicated by a gray line. E) Data from primary as well as metastatic tumor (51 total) sites. Slope = −0.71%, meaning per percent increase in non-modal chromosomes, tumor size was reduced by an estimated 0.71%. F) Data from 29 exclusively metastatic sites. Slope = −0.93%.