Malignant transformation of pulmonary bronchiolar adenoma into mucinous adenocarcinoma: A case report

Figure 1 High-resolution computed tomography. A: A mixed solid and ground-glass nodule (orange arrow, magnified in insert) was present in the posterior basal segment of the lower lobe of the left lung. It measures approximately 17.0 mm × 7.0 mm, was irregular in shape, and was close to the pleura; B: There was a small cystic cavity within the nodule (orange arrow, magnified in insert).

Figure 2 Hematoxylin and eosin staining of the whole tumor. A: The tumor consisted of two general areas (×100): A bronchiole adenoma (BA) (yellow dotted line) area and a mucinous adenocarcinoma (black dotted line) area; B and C: The BA area consisted of a bilayered structure of luminal cells and basal cells that were arranged in glandular, papillary, and flat structures (B: ×100, and C: ×200); D: At high magnification (×400), basal cells (white arrows), ciliated cells (orange arrows) or cubic/Low columnar cells and locally abundant mucinous cells (black arrow), without significant atypia or pathological mitosis, were evident in the luminal epithelium. BA: Bronchiole adenoma; MA: Mucinous adenocarcinoma.

Figure 3 Hematoxylin and eosin staining of the mucinous adenocarcinoma area. A: The tumor was arranged in a glandular structure (×40); B and C: There was a skipping growth pattern around the tissues (B: ×200, and C: ×400); D: It consisted of columnar cells without a clear basal cell layer (×400).

Figure 4 Immunohistochemical staining of the bronchiole adenoma area. A: CK5/6 (×400); B: p40 (×400); C: CK7 (×400); D: TTF-1 (×400); E: Napsin A (×400); F: Ki-67 (×400). CK5/6 and p40 were expressed continuously in the basal cell layer in some areas, and had a discontinuous skipping pattern in other areas. CK7 had diffuse expression in basal cells and luminal cells. TTF-1 was expressed in basal cells, ciliated cells, and cubic cells, but not mucinous cells. Luminal cells had a patchy weak expression of napsin A. The Ki-67 index was low.

Figure 5 Immunohistochemical staining of the mucinous adenocarcinoma area. A: CK5/6 (×100); B: p40 (×100); C: CK5/6 (×400); D: p40 (×400); E: CK7 (×400); F: TTF-1 (×400); G: Napsin A (×400); H: Ki-67 (×400). CK5/6 and p40 were present in a clear boundary at the junction between the bronchiole adenoma and mucinous adenocarcinoma (MA) (A-B, yellow dotted line). The basal cell layer in MA area was completely absent, as shown by staining for CK5/6 and p40, suggesting an invasive disease. The tumor cells were strong diffuse positive for CK7; whereas TTF-1 and napsin A showed only patchy positivity, indicating the differentiation of alveolar epithelial type II cells. The Ki-67 index was low in the infiltrating area.