Background: Chemotherapy is dosed per mg/m², which results in marked differences in inter-patient pharmacokinetics and toxicities. Tailored chemotherapy is based on dose adjustments based on individually recorded toxicities. Previous studies revealed superior survival outcomes with dose dense (DD) adjuvant regimens, but docetaxel was previously not considered suitable in a DD strategy. Health related quality of life (HRQoL) was a secondary endpoint in the Panther study. Methods: Patients with node positive breast cancer (BC), or with node negative BC > 20 mm, receptor negative (Er and Pr) Elston grade III, were randomized between tailored dose dense therapy (E _{38-120 mg/m}²₎ C _{450-1200 mg/m}²₎ followed by four cycles D_{75-100 mg/m}²₎ every second week (three weeks pause between EC and D), G-CSF support and prophylactic antibiotics), the ddtEC-D arm, vs. the control arm (three cycles F₅₀₀ E₁₀₀ C₅₀₀ followed by three cycles of D₁₀₀ every third week). HRQoL was evaluated using EORTC QLQ-C30 + EORTC QLQ-BR23 at baseline and at end of treatment (_˜ 4 months after randomization in both arms). Results: A total of 2017 patients were randomized between February 2007 and September 2011. No statistical differences at baseline for HRQoL. Results, based on 1630 patients (81%), reveal statistical significant differences (p ≤ 0.01) between the randomization arms, favoring the control arm on 13/15 of EORTC QLQ-C30 variables at the end of treatment. For EORTC-BR23, the ddtEC-D arm scored lower on the sexual functioning and chemotherapy side effects subscales. Conclusions: The ddtEC-D arm appeared to have more negative impact on HRQoL than the control arm during therapy. An abstract presenting the results from the main Panther study is also submitted to ASCO 2016. Clinical trial information: NCT00798070 ISRCTN ISRCTN39017665