Peripheral T‐cell lymphoma with diffuse pulmonary infiltration and an increase in serum KL‐6 level

:  Peripheral T-cell lymphoma is a subtype of non-Hodgkin’s lymphoma. A case of peripheral T-cell lymphoma showing diffuse pulmonary involvement together with a marked increase in the level of serum KL-6 is presented. CXR and CT revealed reticular and ground-glass opacities, which mimicked interstitial pneumonia. Immunopathological findings and an analysis of T-cell receptor gene rearrangements of the lung biopsy specimen led to a definite diagnosis of peripheral T-cell lymphoma. In addition, the extensive proliferation of type II pneumocytes, which stained strongly positive for anti-KL-6 antibody suggested that the pneumocytes were the source of serum KL-6.