[Increased level of KL-6 in a BJP-λ-type multiple myeloma patient with poor prognosis]

A 63-year-old female with BJP-multiple myeloma (Durie-Salmon stage III B, International Staging System III) showed an increased level of KL-6, a sialylated carbohydrate antigen that is a MUC1 molecule expressed in type II pneumocytes and reflects activity of interstitial pneumonia. At the time of diagnosis, KL-6 was as high as 22,030 U/ml; however, surfactant protein D (SP-D) was normal, and stroma-related pneumonia was not indicated on CT images. Expression of KL-6 in multiple myeloma cells was detected by immunostaining and the patient was diagnosed with KL-6-positive multiple myeloma. Usually, MUC1 is encoded by chromosome 1q21, but the karyotypic analysis of the patient's bone marrow cells lacked chromosome 1. KL-6 increased as the disease progressed. The patient did not respond to chemotherapy, including bortezomib, showed an increase of pleural effusion, and died. For this patient, multiple myeloma with high KL-6 was refractory to chemotherapy, suggesting that new treatment strategies, including transplantation of hematopoietic stem cells, are required.