Early Lung Cancer With Lepidic Pattern

Adenocarcinoma in Situ, Minimally Invasive Adenocarcinoma, and Lepidic Predominant Adenocarcinoma

Wilko Weichert; Arne Warth

Disclosures

Curr Opin Pulm Med. 2014;20(4):309-316. 

In This Article

The Lepidic Pattern

Until it was suggested to discontinue the use of the term 'bronchiolo-alveolar carcinoma' (BAC),[1] BAC had been used for a broad spectrum of morphologically and molecular diverse tumors, thus leading to confusion and a lack of comparability of study data. The respective growth patterns of former BACs in the stricter sense are now designated as 'lepidic'. There have been considerable discussions about the origin of the term 'lepidic' itself, which were most recently resolved in a historical overview.[21] 'Lepidic' refers to neoplastic tumor cell growth along pre-existing alveolar structures in a flat manner, without forming papillary or micropapillary structures (Figure 1). Lepidic growth is usually accompanied by thickened alveolar walls but typically lacks inflammation. Stromal, vascular or pleural invasion must be absent. The different tumors with lepidic growth are now classified in a continuous spectrum ranging from AAH to AIS to MIA and, ultimately, LPA ( Table 1 ).

Figure 1.

Histomorphological features of atypical adenomatous hyperplasia and adenocarcinoma in situ (AIS). (a) Lepidic growth of an atypical adenomatous hyperplasia (AAH; arrows) adjacent to normal lung (arrowheads). In direct comparison, the nuclei of AAH are enlarged and hyperchromatic but show only mild atypia. The alveolar walls are thickened but invasive tumor growth is not present. From AAH, there is a continuum to morphologic changes usually seen in AIS. (b) In AIS, the size of the nuclei is further increased, the nuclei are usually more hyperchromatic, and there is also a higher degree of variability in cellular and nuclear size and shape (pleomorphism). Although there is no invasive tumor growth, stromal thickening as a reaction to the neoplastic proliferation is evident.

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