Organizing pneumonia with an enlarging tumor-like lesion: immunohistochemical study.

An 86-year-old woman was transferred to our department for investigation of an abnormal enlarging pulmonary shadow with vascular convergence. She had no respiratory symptoms or laboratory data suggesting inflammatory disease. A pulmonary wedge resection was performed under video-assisted thoracic surgery. Pathology examination revealed that the tumor was organizing pneumonia and was composed of fibroblast-like spindle cells, macrophages, lymphoplasma cells, and collagen fibers. Immunohistochemical study revealed that the lesion was in the proliferative state with the relatively more Ki-67-positive fibroblast-like spindle cells. When a surgical resection is necessary for an enlarging abnormal pulmonary mass without any systemic inflammatory reaction or respiratory symptoms, a less invasive approach should be selected.