Clonal changes in inflammatory pseudotumor of the lung. A case report

Background. Pulmonary inflammatory pseudotumor, also known as plasma cell granuloma among many other names, is widely believed to be an inflammatory or reactive lesion rather than a neoplasm, although its pathogenesis is still controversial. Methods. Cytogenetic analysis was performed on a lung mass that showed typical clinical and pathologic features of inflammatory pseudotumor. Ultrastructural and immunohistochemical studies were performed in addition to routine histologic examination. Results. Cytogenetic study of the lesion revealed clonal anomalies of t(1;2)(q21;p23) and del(4)(q27). The patient, a 30‐year‐old woman, presented with an asymptomatic but enlarging right lower lobe mass for which partial right lower lobectomy was performed. The lung mass was well circumscribed radiographically and grossly. Microscopically, it was characterized by a loosely arranged spindle cell proliferation with prominent plasma cell infiltration. Fibroblastic and myofibroblastic differentiation of the spindle cells was demonstrated by ultrastructural and immunohistochemical studies. Conclusion. To the authors' knowledge, this is the first report of clonal cytogenetic changes in a clinically and pathologically typical case of inflammatory pseudotumor in the lung. This finding suggests that pulmonary inflammatory pseudotumor might be a true neoplasm rather than a purely inflammatory or reactive lesion. Cancer 1995; 76:1545‐9.