Antihistamine use and immune checkpoint inhibitor efficacy: An institutional analysis.

e24170 Background: Immune checkpoint inhibitor use has changed the treatment landscape for numerous solid tumor types. Prior work by others has suggested that H1 antihistamine is associated with an improvement in survival among patients receiving immune checkpoint inhibitors for lung cancer. We tested the hypothesis that of patients on a checkpoint inhibitor for any indication, those taking an H1 antihistamine would have longer time on therapy than those who do not. Methods: Deidentified retrospective patient data was collected using Patient Cohort Explorer at University of Mississippi Medical Center. All patients with at least one cycle of pembrolizumab, nivolumab or atezolizumab between 2013 and 2025 were included, as was the subset of patients on one of the aforementioned checkpoint inhibitors plus an oral antihistamine (cetirizine, loratadine, or fexofenadine). Other checkpoint inhibitors were excluded due to insufficient sample size to reasonably maintain anonymity. The primary endpoint was time to treatment discontinuation, measured in cycles, between all those on checkpoint inhibitor and those on checkpoint inhibitor plus an H1 antihistamine. We used this outcome because of its availability in the database. Statistical analysis was performed using unpaired two-tailed T test. Results: Data was collected for 1,182 patients having received a cumulative 9,878 cycles of immune checkpoint inhibitors, including 280 who received concomitant H1 antihistamine. The mean number of immune checkpoint inhibitor cycles delivered to those exposed to H1 antihistamine was significantly higher than those not exposed at 9.9 vs 7.9 (P 0.003, standard deviation 12.1 vs 8.3). Subgroup analysis is presented, with statistical significance demonstrated for pembrolizumab plus antihistamine but not nivolumab or atezolizumab. Sex, race, and insurance status were similar between groups. Conclusions: Our data indicates a positive association between H1 antihistamine use and the number of cycles of immunotherapy a patient receives, suggesting a link affecting the efficacy of immunotherapy. This was demonstrated in a broad population, irrespective of tumor type. Future work will evaluate for associations between H2 antihistamines as well as concurrent chemotherapy administration. All IO w/o AH All IO w/ AH Pembrolizumab w/o AH Pembrolizumab w/ AH Nivolumab w/o AH Nivolumab w/ AH Atezolizumab w/o AH Atezolizumab w/ AH # of patients 901 280 517 155 287 98 97 27 Mean # of cycles* 7.9 +/- 8.9 9.9 +/- 12.1 7.8 +/- 8.6 9.8 +/- 12.1 7.9 +/- 9.3 9.8 +/- 12.1 8.2 +/- 9.7 10.7 +/- 13 Female 371 144 257 92 86 42 28 10 Male 530 136 260 63 201 56 69 17 Median age 62 62 61 61 61 60.5 64 65 White 458 130 235 66 180 52 43 12 Black 422 147 268 88 101 44 53 15 Self pay 72 9 37 4