Health-related quality of life with low-dose pembrolizumab plus chemotherapy in early triple-negative breast cancer: Findings from the PLANeT trial.

607 Background: The PLANeT trial randomized stage II–III TNBC patients to neoadjuvant chemotherapy with or without low-dose pembrolizumab. Primary efficacy end point results were presented at ESMO Congress 2025. QoL was assessed at baseline, mid-treatment, and end-treatment using the EORTC QLQ-C30 across seven domains. Longitudinal changes were analyzed using mixed-effects models with LS-mean estimates and change from baseline at each timepoint. Methods: Stage II–III TNBC patients were randomized in a 1:1 ratio to receive standard NACT with or without pembrolizumab (50 mg Q6W ×3 cycles) prior to surgery. QoL was assessed at baseline, mid-NACT (after 4 cycles), and at the end of NACT (after 8 cycles) using the EORTC QLQ-C30 questionnaire. Seven key QoL domains were analyzed: global health status/QoL (GHS), physical, role, emotional, cognitive, social functioning, and pain. Longitudinal QoL changes were compared between arms using mixed-effects models (MMRM) adjusted for nodal status. Least-squares (LS) mean scores and changes from baseline were estimated for each timepoint. Results: Among 157 patients (median age 49), baseline QoL was high and comparable between arms. QoL declined during neoadjuvant therapy in both groups, with the greatest burden mid-treatment and partial recovery by cycle 8. LS-mean global QoL fell by 14 points in each arm, with no meaningful separation between treatments across any functioning domain. Pain increased in both groups, and financial difficulty peaked mid-treatment before improving by cycle 8. Overall, low-dose pembrolizumab did not compromise QoL compared with chemotherapy alone. Conclusions: Adding low-dose pembrolizumab to neoadjuvant chemotherapy in TNBC did not worsen patient quality of life. The trajectory of functioning and symptom scores was nearly identical to chemotherapy alone, indicating that incorporating reduced-dose immunotherapy does not add to the treatment burden from the patient’s perspective. Clinical trial information: CTRI/2024/01/062088 . Least-squares mean (LS-mean) scores at cycle 8 and changes from baseline for all EORTC QLQ-C30 domains, comparing pembrolizumab + chemotherapy vs chemotherapy alone in the PLANeT trial. Domain Pembro + Chemo (C8 LS-mean) Change Chemo Alone (C8 LS-mean) Change Between-Arm Δ (Change) Global QoL 39.61 −14.19 41.27 −13.61 −0.58 Physical Functioning 73.09 −19.92 74.49 −18.14 −1.78 Role Functioning 85.68 −10.90 85.65 −12.66 +1.76 Emotional Functioning 78.31 −11.11 77.00 −10.34 −0.77 Cognitive Functioning 88.03 −5.99 83.97 −8.44 +2.45 Social Functioning 83.33 −13.04 82.07 −12.87 −0.17 Pain 67.31 +20.73 52.11 +12.45 +8.28