Impact of ABCB1 single‐nucleotide variants on early, extremely severe neutropenia induced by paclitaxel/nanoparticle albumin‐bound paclitaxel in patients with gastric cancer

Aims Paclitaxel and nanoparticle albumin‐bound (nab)‐paclitaxel can cause early, extremely severe neutropenia, occasionally leading to fatal outcomes. As paclitaxel is a substrate of P‐glycoprotein, this study aimed to investigate the impact of ABCB1 single‐nucleotide variants, which encode P‐glycoprotein, on early, extremely severe neutropenia in patients receiving paclitaxel/nab‐paclitaxel plus ramucirumab as second‐line therapy for unresectable advanced/recurrent gastric cancer. Methods We analysed patients treated at Aichi Cancer Center Hospital from January 2018 to August 2023, with DNA samples stored in the Cancer BioBank Aichi. The impact of ABCB1 variants T1236C (rs1128503), G2677T/A (rs2032582) and C3435T (rs1045642) on early, extremely severe neutropenia was examined. Neutropenia was defined as a decline in neutrophil count to <100/μL within 28 days of therapy initiation. Firth's logistic regression evaluated the association between the ABCB1 C3435T (rs1045642) TT genotype and early, extremely severe neutropenia, adjusted for age, sex, baseline neutrophil count, and serum albumin and aspartate aminotransferase levels. Results Of the 203 eligible patients, 5 (2%) experienced neutropenia with neutrophil counts of <100/μL. The odds ratio for neutrophil counts of <100/μL was 28.1 (95% confidence interval 2.8–283.3) in patients with the ABCB1 C3435T (rs1045642) TT genotype. Conclusion The ABCB1 C3435T (rs1045642) TT genotype was significantly associated with early, extremely severe neutropenia in patients receiving paclitaxel/nab‐paclitaxel. Evaluating this genotype status may help predict those at increased risk for early, extremely severe neutropenia.