Cytopathology of pulmonary adenocarcinoma with a single histological pattern using the proposed International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society (IASLC/ATS/ERS) classification

BACKGROUND Guidelines for histological subtyping in patients with surgically resected lung adenocarcinoma (ADC) were recently proposed by the International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society. The objective of the current study was to investigate the cytomorphology of these subtypes of ADC in cases with matched histology specimens demonstrating a single pure subtype. METHODS The authors reviewed their database for patients with histological diagnoses of primary lung ADC with a single histological pattern observed on surgical resection and investigated the cytological findings in 18 matched cytology specimens to eliminate sampling issues in cases of mixed ADC. RESULTS Resections were classified as acinar (7 specimens), solid (6 specimens), lepidic (2 specimens), mucinous (2 specimens), and papillary (1 specimen). Cytology specimens demonstrating a solid pattern had a predominance of 3-dimensional clusters (5 of 6 vs 0 of 12 specimens) (P=.0007, Fisher exact test), necrotic background (3 of 6 vs 0 of 12 specimens) (P=.02), pleomorphic nuclei (6 of 6 vs 1 of 12 specimens) (P=.0004), irregular nuclear contours (6 of 6 vs 3 of 12 specimens) (P=.009), and nuclear enlargement (5 of 6 vs 2 of 12 specimens) (P=.01) compared with the nonsolid patterns. Nuclear pseudoinclusions were present only in nonsolid patterns (5 of 12 specimens), although this finding was not statistically significant (P=.05) CONCLUSIONS Cytological features of lung ADC subtypes proposed by the Study of Lung Cancer/American Thoracic Society/European Respiratory Society classification overlap. However, architectural and nuclear features may be helpful, particularly in distinguishing the prognostically adverse solid pattern from other patterns. Cancer (Cancer Cytopathol) 2015;123:306-17.