84 Chapter 6 Abstract Introduction The World Health Organization Classi cation of Lung Tumors considers “Spread Through Air Spaces” a form of invasion in lung adenocarcinoma. The recently described spread of free- oating cell clusters during lung specimen sectioning, otherwise known as “Spread Through A Knife Surface,” represents an ex vivo artifact. Purpose To prospectively investigate the presence and frequency of these free- oating tumor cell clusters in surgically resected lung cancer specimens and their possible relation to gross examination procedures. A prospective, multi-institutional study of non–small cell lung cancer resection specimen was undertaken. At prosection the first cut was made with a clean knife; the second cut was made in a parallel plane to the first. Four tissue blocks were taken from upper and lower parts of first and second cuts. Hematoxylin and eosin–stained slides were examined for displaced benign and/or malignant tissue fragments. Results Forty-four resection specimens were studied. The mean number of tumor clusters for blocks 1 to 4 was 0.36, 1.44, 1.86, and 1.95, respectively, and for benign fragments was 0.11, 0.11, 0.13, and 0.25, respectively. Almost all cell clusters were intra-alveolar. Comparison of tumor cell clusters in block 1 with blocks 2 to 4 was significant with P-values (Friedman test for repeated measures 0.03) 0.031, 0.02, and 0.05, respectively. Overall, 93% of the loose tissue fragments could be explained by mechanical forces associated with tissue handling. Conclusion While the 2015 World Health Organization Classification of Lung Tumors recognizes Spread Through Air Spaces as a form of lung cancer invasion, such is debatable and, in many instances, likely represents mechanical artifact, including dissemination along the prosecting knife blade.
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