While GBMs are typically resistant to STAT3 inhibition (Fan et al., 2013, 2020; Miyata et al., 2017), both SH5–07 and STAT3 shRNA are specifically toxic to resistant GBM cells in the presence of ispinesib, consistent with the uniform enhancement of IL6-JAK-STAT3 signaling that we observe solely among resistant cells. Here, STAT3 is linked to glioblastoma.