A 74‑year‑old man on the prostate cancer drug apalutamide developed a severe skin rash, fever, very low neutrophil counts, and high eosinophils about six weeks after starting the medication. Stopping apalutamide and treating him with antihistamines, antibiotics, steroids, and a growth factor for neutrophils cleared the rash and normalized his blood counts. He is now being kept on the hormone‑blocking peptide triptorelin instead, with his PSA under control.

Apalutamide is approved for the treatment of nonmetastatic castration-resistant prostate cancer (nmCRPC) and metastatic hormone-sensitive prostate cancer (mHSPC). Currently, the incidence of rash is higher in patients treated with apalutamide. However, the occurrence of apalutamide-associated skin rash combined with apalutamide-induced neutropenia and eosinophilia in a single patient has not been reported previously. The aim of this study is to describe a rare and severe adverse reaction induced by apalutamide, in order to improve clinical awareness and facilitate early recognition and management. Here, we report a case of an mHSPC patient treated with apalutamide who experienced grade 3 rash combined with severe neutropenia and eosinophilia. A 74-year-old male was diagnosed with prostate cancer (cT3bN1M1b) via transperineal prostate biopsy and radiographic examinations. Forty-one days after starting receiving apalutamide, the patient developed a systemic rash accompanied by fever. The routine blood tests indicated that the patient had severe neutropenia and eosinophilia. The condition was diagnosed as an apalutamide-induced drug reaction characterized by rash, severe neutropenia, and eosinophilia. After discontinuing apalutamide, administering antihistamines, providing protective isolation, preventing infection with antibiotics, stimulating neutrophils with recombinant human granulocyte colony-stimulating factor (rhG-CSF), and treating with systemic corticosteroid, the rash completely resolved, and the patient's temperature as well as neutrophil and eosinophil counts returned to normal. The patient is currently receiving intramuscular injections of triptorelin pamoate (15 mg every 3 months), with prostate-specific antigen (PSA) under effective control. Apalutamide-associated rash combined with severe neutropenia and eosinophilia is rare in clinical practice, which not only reduces quality of life but also affects treatment adherence, and can even threaten the life of patients. Therefore, prior to initiating apalutamide treatment, health education should be provided to the patients. During apalutamide treatment, clinical follow-up and management should be intensified. After the occurrence of adverse events, relevant examinations should be performed promptly and early intervention should be implemented.