239 Arguments for pulmonary AIS larger than 7 cm Results The patient from VUmc was a 75-year-old male (Table 1, case 1) showed on CT-scan of the thorax (persistent) diffuse areas of consolidation in his left lower lobe, resulting in a differential diagnosis of infection, localized fibrotic disease or lepidic predominant adenocarcinoma. CT-guided transthoracic biopsy showed adenocarcinoma with a lepidic growth pattern. Surgery was planned and the left lower lobe completely resected. The resection specimen showed a lepidic growth pattern in 12/19 H&E slides from the initially sampled tissue blocks, with no invasive component. As a sharply outlined tumor was lacking and palpation was not supportive in recognizing tumor (Figure 1), additional tissue sampling was performed in the search for possible invasive areas. Eventually, nearly the whole lobe was processed for histologic examination. Including the initial 19 slides, a total of 312 blocks were evaluated. In 281/293 additional slides a similar lepidic growth pattern compatible with AIS as in the initial slides was observed in a background of emphysematous lung (Figure 2A-E). There were no signs of true, nor surrogate markers of, invasion, such as multi-layering or more alveolar filling. In the remaining 12/293 blocks no tumor cells were observed. Figure 1. Gross appearance of case 1. Note on cross sections, no large sharply circumscribed tumor nodus is present, but small greyish-white pinheads, some white fibrosis on the pleural side (left) as well as preexisting emphysematous lung tissue. The red ink on the surface is added during gross examination supporting the analysis of the resection margins in microscopy. The red parenchyma in the middle is not fixed after 1 day submerging in fixative (low diffusion rate66) 16
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