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passages: 4.2. Histological Findings
  Microscopy revealed features of a diffusely growing discohesive carcinoma, exclusively growing in the alveolar interstitium, thus expanding it, while leaving the original alveolar architecture intact (Figure 2). There was local ulceration of the pleura, while, beyond this ulcer, the tumor formed a thick cake of discohesive tumor cells lining the pleural membrane (Figure 2(c)), with only focal, microscopic invasion into the fatty tissue of the parietal pleura.
  The tumor consisted of atypical, moderately polymorphous, and irregularly shaped tumor cells with marked discohesiveness. They featured scant eosinophilic cytoplasm and irregularly contoured and hyperchromatic nuclei, often containing one or more prominent nucleoli (Figure 2(b)). There were many mitoses and apoptoses present, but necrosis was not observed. No squamous or glandular differentiation was observed, and mucin stains (PAS-D and alcian blue) were negative. Within the tumor, there were multiple small blood-filled clefts and blood lakes. Angioinvasion in medium-sized vessels, including an artery, was demonstrated (Figure 2(d)).
  Of note, the broadened alveolar septa were lined by markedly atypical epithelial cells, yet less atypical than the interstitial carcinoma (Figures 2(a) and 2(b)). The atypia of the lining cells extended beyond the tumor front, showing a sharp demarcation with normal type I pneumocytes (Figure 2(a)), a feature characteristic to nonmucinous adenocarcinoma in situ with lepidic growth pattern (former bronchioloalveolar carcinoma, BAC) [3].
  