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Secondary bronchiolitis obliterans-organizing pneumonia (BOOP) is a reaction to injury, forming granulation tissue with airspaces. Idiopathic cryptogenic organizing pneumonia (COP) and secondary BOOP are histologically similar. COP has been reported to show increased collagen in the granulation plugs and fewer myofibroblasts and capillaries. Using CD34 for capillaries and alpha-smooth muscle actin for myofibroblasts, we assessed these statins to differentiate COP from secondary BOOP.