CTCL patient–isolated malignant cells and CTCL cell lines show variable sensitivity to a panel of targeted therapeutic agents. Isolated malignant cells from patient samples (n = 19), control samples (n = 5), and established CTCL cell lines (n = 5) were incubated with a range of concentrations of ruxolitinib, mivebresib, venetoclax, vorinostat, or bortezomib for 72 hours, from which IC₅₀ values and Hill slopes were calculated. (A) Comparison of IC₅₀ values. CTCL patient samples, control samples, and CTCL cell lines revealed statistically significant differences in response to mivebresib and bortezomib. (Bi) CTCL patient samples in order of IC₅₀ of ruxolitinib. Patients were grouped as high-responders and low-responders to ruxolitinib at an a priori cutoff of 1 µM. The median and mean IC₅₀ for patient samples were 2.16 µM and 79.47 µM, respectively. (Bii) IC₅₀ differences for B1 and B2 stage to ruxolitinib were found to be nonsignificant. (Biii) Hill slope differences of CTCL patient samples and CTCL cell lines to ruxolitinib. (C) Dose–response curves for patient samples (C) and CTCL cell lines (D) for ruxolitinib (i), mivebresib (ii), venetoclax (iii), vorinostat (iv), and bortezomib (v). *P < .05; **P < .001. ns, not significant.