Discrepancies Between Morphological and Immunohistochemical Classifications Are Associated With Prognoses and Subtypes of Lung Cancer.

Abstract

Immunohistochemical (IHC) staining has been routinely used to distinguish adenocarcinoma (ADC) and squamous cell carcinoma (SCC) of the lungs; however, it is challenging to obtain an accurate diagnosis, especially for cases with discrepancies between IHC and hematoxylin and eosin (H&E) staining results. This study aimed to clarify the clinicopathological characteristics of these discrepant cases. Tissue microarray specimens from 321 patients with ADC and SCC were used for H&E and IHC staining of thyroid transcription factor 1 (TTF-1), Napsin A, cytokeratin 5/6 (CK5/6), p40, and p63. The pathological diagnosis was made based on (1) H&E, (2) IHC, and (3) both H&E and IHC results. Discrepant cases were defined as those with different diagnoses based on the H&E and IHC results. A total of 32 (10%) discrepant cases were identified. ADC (3.9%) showed fewer discrepant cases than SCC (51%). Discrepant cases of ADC had a significantly higher proportion of poorly differentiated tumors and subtypes of solid and invasive mucinous ADC, and they also had shorter overall and disease-free survival than concordant cases. Solid and invasive mucinous ADC cases showed low positivity for TTF-1 (84% and 40%, respectively) and Napsin A (88% and 80%, respectively), and invasive mucinous ADC cases showed high positivity for CK5/6 (80%). The sensitivity and specificity of TTF-1+Napsin A for ADC were 91% and 83%, respectively, whereas those of CK5/6+p40 for SCC cases were 90% and 96%, respectively. Discrepant cases of ADC are associated with solid and invasive mucinous subtypes and shorter survival.