[1951] Complex Acinar Pattern: A Distinct Morphologic Subtype and a Poor Prognostic Indicator in Primary Lung Adenocarcinoma

Congli Wang, Heba Y Durra, Yajue Huang, Varsha Manucha. Temple University Hospital, Philadelphia, PA

Background: The newly proposed IASLC/ATS/ERS classification of lung adenocarcinoma has emphasized the prognostic significance of histologic subtyping. In this study two surgical pathologists evaluated the histological patterns of primary lung adenocarcinoma in different stages. The predominant patterns were correlated with established histological prognostic markers and tumor stage.
Design: 49 cases of lung adenocarcinoma diagnosed between 1998 to 2012 were retrieved from our archives. The H&E stained slides were evaluated by two surgical pathologists (VM and HD), 17 cases together and 32 cases independently. Histologic subtyping was performed according to the IASLC/ATS/ERS classification, each histologic component was recorded in 5% increments and the predominant pattern was defined as the one with the highest percentage. Tumors were staged based on the AJCC 7th edition. Cohen's kappa, k was calculated to evaluate the agreement between reviewers. The potential association of various patterns with established prognostic histologic parameters was assessed by chi-square.
Results: The two raters agreed on the predominant pattern in 23 out of 32 independently reviewed cases (k=0.634), and had different opinions on 9 cases including 2 cases of acinar vs papillary and 2 cases of acinar vs lepidic. In the remaining 5 cases, the disagreement was between acinar and a more complex pattern consisting of irregular, jagged, fused, closely packed glands with cribriform architecture, designated as complex acinar pattern in this study. Accordingly 4 cases were reclassified into this pattern. On correlation, 24 solid and micropapillary predominant tumors were associated with high mitotic count (> 5/10HPF; p=0.0003; ranging 6-54/10HPF) and severe cytologic atypia (p=0.0034), but not with higher stage (beyond IA; p=0.0599) and vascular invasion (p=0.2124). The association became more significant (higher stage: p= 0.0067; high mitotic count: p<0.0001; severe cytologic atypia: p= 0.0020; vascular invasion: p=0.0017) after combining tumors with predominant complex acinar pattern.
Conclusions: Agreement on the predominant histologic pattern was good between two pathologists despite minor disagreements in quantitative assessment of patterns. Tumors with complex acinar pattern may behave completely different form those with classic acinar pattern and should be recognized as a distinct subtype. A more detailed description of this pattern in the classification system and a large-scale study to evaluate its prognostic significance are indicated.
Category: Pulmonary

Monday, March 4, 2013 1:00 PM

Poster Session II # 289, Monday Afternoon


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