Histology of the BML. (a) A well-circumscribed leiomyoma mass in the normal lung parenchyma (H & E, ×12.5). (b) The mass is positive for Masson’s trichrome stain. It reveals that the tumor is of smooth muscle nature (Masson’s trichrome, ×12.5). (c) Benign-appearing spindle-shaped cells arranged in intersecting fascicles (H & E, ×400). Immunohistochemical staining was positive for: (d) smooth muscle actin (×400), (e) desmin (×400), (f) estrogen receptor (× 400), and (g) progesterone (×400). (h) Ki-67 is less than 1%, signifying a low proliferate status and a benign nature (×200).