Napsin A: Utility in Identifying Primary Mucinous Lung Adenocarcinomas Versus Mucinous Metastasis
Deirdre E Amaro, Grace Y Lin. UC San Diego Health Care System, San Diego
Background: Mucinous types of primary lung adenocarcinoma (including mucinous bronchioloalveolar) often present a challenge with lack of staining for traditional lung markers (e.g. TTF-1) and variable staining for CK7 and CK20. They may be difficult to distinguish from metastatic mucinous adenocarcinomas of the gastrointestinal tract and ovary. Napsin A is an aspartic proteinase that appears to be involved in the maturation of surfactant protein B and has been shown to be superior in sensitivity and comparable in specificity to TTF-1 for lung primary adenocarcinomas. The question remains, however, if Napsin A retains its usefulness for pulmonary adenocarcinomas with mucinous differentiation, the variants which are notorious for being morphologically and histochemically difficult to distinguish from metastatic adenocarcinoma (usually of colorectal origin). Inamura et al. found that immunoreactivity for Napsin A was lost in all 7 of the pulmonary adenocarcinomas with enteric differentiation that they examined. This study further examines Napsin A immunoreactivity in mucinous pulmonary adenocarcinoma in comparison to mucinous adenocarcinomas of the ovary, appendix and colon.
Design: A total of 40 cases of mucinous adenocarcinoma specimens (21 lung primary, 12 colorectal/appendiceal, 7 ovarian) were identified by computerized searches of pathology reports. Cases were selected regardless of age, gender, or ethnicity, spanning from 2000-2011. Napsin A, TTF-1, CK7, and CK20 immunohistochemical stains were performed on selected formalin-fixed paraffin embedded (FFPE) cell blocks. Slides were grouped by immunostain, randomly sorted, and blinded before review. Each slide was graded on stain intensity (0-3+) and percentage of tumor cells stained.
Results: See Table 1.