121 Significance of loose tumor cells in pulmonary arteries Adenocarcinoma subtypes (n=40)b AIS 3 (8%) Lepidic 13 (33%) Papillary 0 (0%) Acinar 6 (15%) Micropapillary 2 (5%) Solid 16 (40%) Comments: a 4 patients with 2 wedge excisions in the same surgical procedure; b 4 patients with 2 tumors in 2 wedges, 1 patient with 2 tumors in a lobectomy and 1 in wedge, 2 patients with a double tumor in lobectomy Abbreviations: SD = standard deviation; AIS = adenocarcinoma in situ Microscopic findings All the histological sections contained alveolar walls covered with tumor cells located near branches of the pulmonary artery. Frequently, in the routine H&E stain, a few clusters of tumor cells, focal remaining erythrocytes, and rare alveolar macrophages, were observed. The cytonuclear appearance of the tumor cells in the arterial lumen was similar to the adjacent alveolar wall lining tumor cells. Immunohistochemical staining with CK7, which is reactive to the cytoplasm of most pulmonary adenocarcinomas, revealed immunohistochemical positive single tumor cells or small clusters in the ‘looking like air’ partially empty lumen of the larger pulmonary arteries, without fibrin (Figure 1). This finding was present in 41 out of 74 (55%) histological sections, 26 out of 40 (65%) tumors and in 23 out of 33 patients (70%). In the smallest branches of the pulmonary arteries tumor cells were not discerned. Intravascular tumor cells were found in 2 of the 3 of tumors without invasion (AIS) (67%) and in 19 of the 37 tumors (51%; P=0.61) with invasion. No tumor cells were observed neither in venous, nor in lymphatic vascular structures. 10
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