To determine whether the alternative inclusion of ECT2-Ex5 may have relevance to chemotherapy resistance in breast cancer patients, we quantitated ECT2 Ex5+ and Ex5- isoforms (as well as total ECT2 mRNA) by RT-qPCR in a collection of 526 clinically annotated breast tumors that were collected before they were treated with or without chemotherapy, which in 95% cases used Doxo or the highly related eprirubicin (Supplementary Table S2). Here, ECT2 is linked to breast cancer.