Mecapegfilgrastim for Prevention of Chemotherapy-Induced Neutropenia in Advanced Breast Cancer

This prospective, real-world observational registry study will evaluate the effectiveness and safety of mecapegfilgrastim for the prevention of chemotherapy-induced neutropenia in patients with advanced breast cancer receiving chemotherapy. The decision to use mecapegfilgrastim will be made by the treating physician as part of routine clinical care. Participants will be followed to collect information on neutropenia, febrile neutropenia, treatment-related adverse events, and chemotherapy delivery.

Inclusion Criteria: * Age 18 years or older. * Histologically confirmed advanced breast cancer, defined as locally recurrent disease not suitable for curative treatment or metastatic disease. * First recurrence or metastasis, or documented disease progression during palliative treatment, with a planned new systemic anticancer treatment regimen. * Estimated life expectancy of at least 3 months. * Ability and willingness to provide written informed consent. Exclusion Criteria: * Early-stage breast cancer. * Ongoing systemic anticancer treatment without a need to change to a new treatment regimen. * Pregnant or breastfeeding women. * Any condition or other reason that, in the investigator's judgment, makes the participant unsuitable for enrollment.