Basophil activation test (BAT) is valuable for pheno-endotyping hypersensitivity reactions to chemotherapeutics in negative skin test allergic type-I people, particularly in those suffering from moderate/severe hypersensitivity reactions. This study sought to determine BAT utility in patients reporting immediate hypersensitivity reactions to taxanes and platinum compounds during 2020-2022.

Clinical history and skin tests (clinical phenotyping) were used to categorize patients into Type-I, Cytokine release reaction, or Mixed groups. As per Brown's classification, severity was determined. A total of 30 unaffected, non-exposed controls were also incorporated. Those who had mild- to moderately negative skin tests had a drug provocation test, and BAT was administered to all the participants.

In total, 90 patients were prospectively included. Out of these, 31 patients experienced reactions to taxanes (18 Docetaxel/13 Paclitaxel) and 59 patients experienced reactions to platins (30 Carboplatin/23 Oxaliplatin/6 Cisplatin). Finally, 65.4% of them were identified as allergic. Hypersensitivity reactions were consistent with Type-I in 37.1% of patients, cytokine release reaction in 41.3%, and mixed in 21.6% of participants.

The majority of patients (63%) experienced mild responses. In 55.3% of allergic people, BAT was positive, while it was negative in all non-allergic patients and controls. BAT specificity and sensitivity were 95.5% and 53.8% respectively, with an important association with skin test (r=0.7). Notably, 63% of moderate, 34% of severe, and 3% of mild hypersensitivity reactions were positive for BAT. In the study, 60% of Type-I, 30% Mixed, and 10% of individuals with cytokine release reaction tested positive for BAT.