Napsin A is a useful marker for metastatic adenocarcinomas of pulmonary origin

To address whether napsin A is useful for identifying metastatic adenocarcinomas of pulmonary origin.

Fifty-four cases of adenocarcinoma that metastasized from the lungs to various sites and 1762 cases of carcinoma from various organs were immunostained for napsin A, TTF-1, CK7, CK20 and CDX2 using tissue microarray. The expression patterns of napsin A and TTF-1 in metastatic pulmonary adenocarcinomas were compared with matched primary lung tumours. Napsin A and TTF-1 were expressed in 87.0% and 81.5% of the metastatic pulmonary adenocarcinomas, respectively. Although there was no significant difference in the positivity of napsin A and TTF-1 as a single marker in metastatic pulmonary adenocarcinomas, the expression scores for napsin A were much higher than those for TTF-1 (P < 0.001). Moreover, the positivity and expression scores of napsin A in primary pulmonary adenocarcinomas were maintained in metastatic adenocarcinomas better than TTF-1. Most non-pulmonary adenocarcinomas were negative for napsin A, except for renal cell carcinomas (13.4%), ovarian adenocarcinomas (7.1%) and uterine endometrial adenocarcinomas (14.5%). In particular, clear cell adenocarcinomas of ovary (68.8%) and uterus (66.7%) frequently expressed napsin A.

These data suggest that napsin A may be a useful marker for identifying metastatic adenocarcinomas of pulmonary origin in combination with TTF-1.