Acute myeloid leukemia presenting as a pulmonary mass in a 70-year-old: a diagnostic challenge

Abstract Background Acute myeloid leukemia (AML) occasionally presents with extramedullary disease, but pulmonary involvement is rare and often misdiagnosed as primary lung carcinoma, particularly in chronic smokers. Accurate diagnosis requires histopathology supplemented by immunohistochemistry (IHC). Case presentation We report a 70-year-old chronic smoker who presented with cough, chest pain, weight loss, and a right hilar lung mass. Initial histology of a lung biopsy was suspicious for small-cell lung carcinoma (SCLC). However, laboratory findings revealed progressive cytopenias and circulating blasts. Bone marrow evaluation demonstrated florid myeloblast proliferation consistent with AML. Further IHC of the lung biopsy confirmed myeloid lineage (CD34 positivity, MPO, CD117) and excluded neuroendocrine or epithelial carcinoma markers (TTF-1, synaptophysin, chromogranin, cytokeratin AE1/AE3). A final diagnosis of AML with pulmonary involvement was established. Despite diagnosis, the patient deteriorated rapidly and died before initiation of therapy. Conclusion This case highlights the diagnostic dilemma of AML masquerading as primary lung cancer in smokers. It underscores the indispensable role of IHC in distinguishing hematologic malignancies from solid tumors, thereby avoiding misdiagnosis and inappropriate management. Clinicians should maintain a high index of suspicion for hematologic disease when atypical laboratory findings accompany pulmonary masses.