LAUSR

An 86-year-old man presented with blasts in peripheral blood and thrombocytopenia. His medical history included lung cancer and esophageal cancer, which had been detected on PET-CT in the previous year. Esophageal cancer (squamous cell carcinoma, T2N0M0) was pathologically diagnosed, and the patient was treated with local radiotherapy (total dose: 50.4 Gy) and 2 courses of less-intensive 5-fluorouracil (5-FU) chemotherapy, based on his condition. Bronchoscopy revealed that there was no malignancy, and Mycobacterium avium was isolated from the patient’s bronchoalveolar lavage fluid. Eleven months after the diagnosis of esophageal cancer, blasts appeared in the patient’s peripheral blood, and leukemia was suspected. A bone marrow (BM) examination showed a blast percentage of 84%, and the blasts had severely dysplastic nuclei (Fig. 1a). The blasts were negative for periodic acid-Schiff, peroxidase, and alpha-naphthyl butyrate esterase. Flow cytometry showed that the blasts in the CD45 + gate were positive for CD7 (99.5%), CD13 (73.8%), CD19 (81.6%), CD33 (94.6%), CD34 (99.6%), CD56 (99.4%), and HLA-DR (91.6%) and negative for CD3, CD10, and CD14. Immunohistochemical examinations of BM biopsy samples confirmed that the blasts were positive for CD19, CD79a, CD71, CD34, CD56, cytoplasmic CD3 epsilon, and p53 and negative for surface CD3 epsilon and PAX5. To rule out the possibility of BM carcinoma, the cells were stained with AE1/3, CAM5.2 antibody, and anti-cytokeratin (CK)19 antibody. Surprisingly, the blasts stained positive for CAM5.2 antibody, producing a dot-like pattern (Fig. 1b), but not for AE1/3 or the CK19 antibody. Further examinations for CK expression showed that the cells were positive for CK18 (Fig. 1c), and negative for CK8. The CAM5.2 positive rate was 38.4% and CK18 positive rate of 21.4% when 1000 blasts were counted using two continuous sections stained with CAM5.2 or CK18 antibodies, respectively. Chromosomal analysis showed a complex karyotype, which mainly involved triploidy. A diagnosis of therapy-related leukemia with aberrant CK expression after radiotherapy and 5-FUbased chemotherapy was made. p53 overexpression in therapy-related leukemia is related to p53 mutations and a complex high-risk karyotype. Aberrant CK expression on leukemic cells is extremely rare. However, blasts obtained from a patient who developed therapy-related MDS after breast cancer reacted with the CAM5.2 antibody. Other studies have reported that small subsets of lymphomas and plasma cell neoplasms, but not leukemia, expressed CK. In our patient, the leukemic cells were positive for CAM5.2 and CK18 antibodies, indicating