PMC8019666_01
CT showed a 1.5cmx1.4cm mass in the middle lobe of the right lung, closely related to the bronchi (A, red arrow). The tumor is mainly composed of lepidic-growing mucinous cells with papillary structures and abundant intra-alveolar mucus (B, 200x). The skipping growth pattern of tumor cells can be noticed (C, 200x). In certain glandular areas, the presence of basal cell layers could not be ruled out (D, 200x). A mixture of ciliated cells and columnar cells could be observed in the glandular area (E, 200x). No distinct boundary was found in the junctional zone between the glandular and the lepidic areas (F, 100x).
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Tomography (CT) revealed a 1.5cmx1.4cm nodule in the middle lobe of the right lung. The lesion was lobulated, with spicule formation, associated with distal airway tracts (Figure 1A, red arrow). Microscopically, the tumor was mainly composed of two patterns: glands lined with proliferative mucinous cells and tall columnar mucinous cells growing along the alveolar wall (Figure 1B). Based on the skipping growth pattern seen in certain areas (Figure 1C), the intraoperative pathological diagnosis favored IMA. The luminal layers of the glands were lined predominantly by cuboidal cells, interpreted by ciliated cells and columnar cells (Figure 1D). Intraluminal papillaries composed of mucinous cells could be noted in certain glands. (Figure 1E). No distinct boundary was found between the glandular and the lepidic areas (Figure 1F). Furthermore, these two distinct areas were micro-dissected and analyzed by a panel covering EGFR, ALK, ROS1, KRAS, NRAS, PIK3, HER2, and BRAF (Supplementary Figure 1).
Hematoxylin-eosin (HE) and P40 stain of the glandular area with continuous basal layer, an area of 5x3 mm2 was demonstrated (A and B, 40x). The cuboidal and columnar cells in the luminal layer were TTF-1 positive (red arrows; C, 100x). Loss of continuity of the basal cell layers at the BA to IMA junctional zone: red arrows indicate the continuous basal cell layer; purple arrows indicate the sporadic staining of basal cell marker in the junctional area; black arrows indicate the absence of basal cell layer (D-F, 200x).
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The expression of p40, p63, and CK5/6 demonstrated an area composed of continuous basal layer measuring 5x3 mm2 (Figure 2A and B). TTF-1 was positive in the columnar and cuboidal cells in the luminal layer of the glands (Figure 2C, red arrows). Interestingly, in the adjunct lepidic areas, basal cells were absent, as demonstrated by the negative staining of basal markers (Figure 2D-F, black arrows). In the junctional zone, p63, p40, and CK5/6 showed only sporadic expression (Figure 2D-F, purple arrows).
Quantitative reverse-transcript polymerase chain reaction (qRT-PCR) revealed the same KRAS mutations (G12V) in both BA (A) and IMA (B).
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The same KRAS mutations (G12V) in both portions were identified (Figure 3), supporting the identical cellular origin of both parts.