Case Report: Life-threatening neutropenia with absolute neutrophil count of zero after low-dose regional arterial infusion chemotherapy to lung in a patient with advanced triple-negative breast cancer after multiple lines of treatment

Background The risk of severe myelosuppression following regional arterial perfusion chemotherapy in heavily pre-treated patients is often underestimated, especially when pre-treatment hematologic status appears adequate. This case highlights the unexpectedly profound bone marrow toxicity that can occur under these circumstances and details the critical management strategies required. Case presentation We report a case of a 51-year-old female patient with advanced triple negative breast cancer (TNBC) who developed severe myelosuppression following regional arterial perfusion chemotherapy, despite the chemotherapy dose being lower than the standard systemic dose. The patient had grade I myelosuppression before regional arterial perfusion chemotherapy; however, after perfusion with albumin paclitaxel and gemcitabine, she developed life-threatening severe myelosuppression, with absolute neutrophil count (ANC) dropping to 0 and remaining ≤0.01×10 9 /L for 3 consecutive days. Timely administration of granulocyte colony-stimulating factor (G-CSF), antibiotics, and supportive care effectively reversed the myelosuppression and prevented infection. Due to chest tightness and dyspnea caused by the massive pleural effusion, thoracentesis drainage was decisively performed when the white blood cell count showed an upward trend (neutrophil count, 0.06×10 9 /L). The procedure was smooth and without complications. Conclusion This case underscores that locoregional chemotherapy, even at reduced doses, can cause profound myelosuppression in extensively pre-treated patients. It also illustrates that a pre-treatment ANC within the normal range may not reliably reflect bone marrow reserve in this population. Prompt, intensive supportive care—including prophylactic antibiotics, G-CSF, and protective isolation—is essential. In carefully selected patients during early hematologic recovery, under strict infection prevention measures and multidisciplinary evaluation, invasive procedures such as thoracentesis may be feasible.