Bronchiolitis obliterans-organizing pneumonia (BOOP) is an inflammatory and fibrosing disease involving the distal bronchioles, bronchiolar ducts, and alveoli. We studied 91 patients with BOOP. Univariate analysis was used to relate age, sex, smoking, morphology, and expression of immunohistochemical markers CD68, D2-40, CD31, CD34, collagen IV, collagen III, platelet-derived growth factor receptor, and vascular endothelial growth factor (VEGF) with the response to corticosteroid therapy. Seventy-two patients had idiopathic BOOP and 19 secondary BOOP. The median age of the patients was 59.54 years. Most patients were current or former smokers. All cases had a patchy lesion consisting of small buds of fibromyxoid tissue in small bronchioles, bronchiolar ducts, and alveoli. The buds contained collagen and reticulin fibers, fibroblasts, macrophages, mononuclear inflammatory cells, and vessels in different proportions. We found no morphologic differences between primary and secondary BOOP. Patients younger than 38 years and nonsmokers had a significant good response to corticosteroid therapy. Favorable morphologic predictors were the presence of large bronchial plugs and mild inflammatory reaction (P = .093). By immunohistochemistry, the presence of collagen IV with the absence of collagen III, CD68-positive cells and positive VEGF were associated with a good response to corticosteroid therapy. We conclude that age, smoking, localization, and extension of proliferative intrabronchiolar plugs and positive immunostains for CD68, VEGF, and collagen IV with negative collagen III were useful to predict response to corticosteroid therapy and relapse.
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