Delayed hypersensitivity reaction related to the use of pegfilgrastim

Filgrastim and pegfilgrastim are granulocyte colony-stimulating factor products, which have been part of the supportive treatment of cancer patients for years to increase the white blood cell count and absolute neutrophil count with the objective of preventing neutropenic fever in patients at risk because of chemotherapy. Pegfilgrastim is a glycosylated form of filgrastim with a prolonged duration of effect, a reduced renal clearance, and relatively fewer side effects. We present a patient with early breast cancer who developed a rash more than a week after the use of pegfilgrastim. Clinicians must be aware of the possibility of a delayed hypersensitivity reaction as the application of this drug is increasing and an adverse event can result in delay of chemotherapy treatment.