Severe neutropenia probably caused by enzalutamide and abiraterone in a prostate cancer patient

Abiraterone and enzalutamide are two androgen receptor pathway inhibitors approved, among others, for the treatment of metastatic castration-resistant prostate cancer in adult men whose disease has progressed on or after a docetaxel-based regimen. Although hematological effects, especially neutropenia, are one of the main complications of other oral antineoplastic drugs, these adverse effects are infrequent in the case of androgen receptor pathway inhibitors.

We report the case of a patient diagnosed with metastatic castration-resistant prostate cancer who discontinued an androgen receptor pathway inhibitor due to drug-related grade 4 neutropenia. His control blood counts before enzalutamide starting were normal. After one month of treatment, he developed a grade 4 neutropenia, with complete neutrophil count recovery four weeks later. He underwent a bone marrow aspiration, which revealed normocelullar results, and enzalutamide was restarted. Three weeks later, the treatment was eventually discontinued due to neutropenia reappearance. Neutrophil count recovery was achieved one month later. Then, he started treatment with abiraterone, but two weeks later neutropenia reappeared. Abiraterone was withdrawn, and the patient recovered from neutropenia 2 weeks later.

This case exposes not only the occurrence of rare toxicity of two individual drugs but also the description of a probable drug-class adverse event not reported before. The patient recovered from neutropenia after the androgen receptor pathway inhibitor was withdrawn, thereby supporting the diagnosis of probable drug-induced neutropenia.

There is scarce evidence in the literature concerning androgen receptor pathway inhibitor-related neutropenia. However, its life-threatening potential cannot be ignored, so healthcare professionals should be warned of the possibility of the occurrence of such adverse reactions.