Erlotinib-induced complete remission in AML lacking EGFR expression. (A) Pretreatment bone marrow with up to 90% of cellularity composed of myeloid blasts (hematoxylin-eosin; magnification, × 400). Insert: Wright-Giemsa stain, magnification × 1000 oil. (B) Fine-needle aspiration cytology of the lung mass reveals 3D cohesive clusters of atypical epithelial cells containing intracytoplasmic mucin vacuoles, consistent with adenocarcinoma (hematoxylin-eosin; magnification, × 1000 oil). (C) Graph of peripheral blood counts over time. From weeks 1 to 8, patient remained pancytopenic with AML. Three weeks after starting erlotinib therapy, patient's absolute neutrophil count (ANC) and hemoglobin (Hgb) normalized, while platelet counts exceeded 100 × 10⁹/L. Complete remission was documented by bone marrow biopsy on week 20 (panel D). Peripheral counts show recovery after each round of combination chemotherapy for NSCLC (arrows), suggesting adequate marrow reserve while remaining in complete remission. (D) Posterlotinib bone marrow with variable (average 30%) cellularity and trilineage maturing hematopoiesis. Myeloblasts are less than 3% (hematoxylin-eosin; magnification, × 200). Insert: magnification, × 400. (E) Immunohistochemical staining of initial bone marrow biopsy for EGFR. Only stromal cells (arrowheads) stain positively. Myeloblasts are EGFR negative (magnification, × 1000 oil). Images were acquired using an Olympus BX51 microscope (Olympus, Tokyo, Japan) equipped with either a 20×/0.5 NA, 40×/0.65 NA, or 100×/1.3 NA oil objective and mounted DP12 digital camera, and were further processed (cut out and white balanced) with Adobe Photoshop CS2 (Adobe Systems, San Jose, CA).