Microscopically, the tumor cells similar to those occurring in the bladder were found beneath the respiratory epithelium of the trachea (Fig. 4a-c) that were negative for CK(AE1/AE3) (Fig. 4d), TTF-1 and P63, while were positive for CD21, CD23 (focal), and CD35 (focal) (Fig. 4e, f) by immunohistochemistry. Here, CR2 is linked to neoplasm.