Introduction Granulocyte colony-stimulating factors (G-CSF) are utilized both in the treatment and prophylaxis of chemotherapy-induced neutropenia. Lipegfilgrastim is a long-acting G-CSF. Albeit it provides ease of administration compared to short-acting GCSFs, some lipegfilgrastim-related adverse events may occur. Bone pain, widespread body pain, and feeling of fever are among common adverse effects, while rare but more serious adverse effects such as leukocytosis, spleen rupture, interstitial pneumonia, acute respiratory distress syndrome, capillary leak syndrome, hypokalemia, and glomerulonephritis may occur as well. Case report We reported a case of hyperleukocytosis that developed due to prophylactic administration of lipegfilgrastim following the first course of neoadjuvant pertuzumab (840–420 mg), trastuzumab (8–6mg/kg), and docetaxel (75 mg/m2) in a 45-year-old female patient with a diagnosis of breast invasive ductal carcinoma. The patient, who presented with weakness, loss of appetite, and oral intake disorder, had elevated white blood cell (WBC), lactate dehydrogenase (LDH), and uric acid levels in her test results. Peripheral smear (PS) had a left shift. Management and outcome Intravenous 0.9% NaCl and peroral allopurinol were started to be administered to the patient. On the ninth day of hospitalization, the patient's clinical manifestation improved, and her WBC, LDH, uric acid, and PS returned to normal. Besides, the progression to tumor lysis syndrome (TLS) was prevented by appropriate hydration and allopurinol treatment. In subsequent chemotherapies (CTs), lipegfilgrastim was discontinued and filgrastim was started. The patient whose hyperleukocytosis did not recur was operated on following neoadjuvant CT. The patient's routine follow-up continues without any problems. Discussion Although lipegfilgrastim-induced hyperleukocytosis has not been reported in the literature, it should be borne in mind that hyperleukocytosis and related complications may occur, as in our case.
