Fig. 1(A) Nonmucinous adenocarcinoma in situ. (B) Tumor shows continuous growth of neoplastic cells along the slightly thickened alveolar septa without disruption of the alveolar structures. (C) Equivocal invasion showing alveolar collapse. Tumor has a central scar (arrow) with a peripheral lepidic growth pattern. (D) The central scar demonstrates thick fibrous septa with intact tumor glands, but less identifiable alveolar architecture and plump, reactive fibroblasts. Some pathologists interpreted a desmoplastic stroma associated with tumor invasion, whereas others considered the same features as benign scarring/fibroelastosis in Thunnissen's reproducibility study.13 (E) Nonmucinous minimally invasive adenocarcinoma. Tumor consists predominantly of lepidic growth with a small invasion focus (arrow). (F) Tumor acini and single cells are invading in the desmoplastic stroma with chronic inflammatory cells.
Table 1.Emerging issues in IASLC/ATS/ERS classification of lung adenocarcinoma in resected specimens with respect to both histologic subtyping and invasion
Emerging issues |
I. Histologic subtyping |
1. Reproducibility |
2. Potential parameters for subtyping formulation |
1) Impact of aggressive minor pattern |
2) Subdivision of comprehensive subtyping |
3) Other grading system: mitosis, nuclear grade |
3. Candidate for additional subtype: ragged/fused glands and cribriform pattern |
II. Invasion |
1. Determination of invasion |
2. Extent of invasion |
1) Percentage versus cutoff size |
2) Impact of scar size or stromal desmoplasia and inflammation |
3. Additional factors to be considered |
1) Significance of aggressive component |
2) Outcome of patients with MIA histology greater than 3 cm |
3) Lepidic growth versus aerogenous spread of invasive carcinoma |
Table 2.Summarized diagnostic criteria of five predominant patterns for invasive adenocarcinoma in resected specimens according to the new IASLC/ATS/ERS classification3,14
Pattern |
Diagnostic criteria |
Lepidic |
Neoplastic cells growing along pre-existing alveolar structures |
|
Common septal widening with sclerosis |
|
Absence of papillary or micropapillary patterns and intra-alveolar tumor cells |
Acinar |
Glands which are round to oval-shaped with a central luminal space surrounded by tumor cells |
|
Cribriform arrangement |
Papillary |
Growth of columnar cells along central fibrovascular cores |
|
Papillary structures filled with alveolar spaces, even a tumor has lepidic growth |
Solid |
Polygonal tumor cells forming sheets which lack other recognizable patterns of adenocarcinoma |
Micropapillary |
Tumor cells growing in micropapillary tufts which lack fibrovascular cores |
|
Detached and/or connected tumor cells to alveolar walls |
|
Floating ring-like glandular structures within alveolar spaces |