The use of placental S100 (S100P), GATA3 and napsin A in the differential diagnosis of primary adenocarcinoma of the bladder and bladder metastasis from adenocarcinoma of the lung.

Primary bladder adenocarcinoma accounts for 0.5-2% of all malignant bladder tumours. Literature data indicate the bladder as the second most common site of metastatic genitourinary tumours, with the kidney as the most frequent location. Secondary tumours of the bladder account for about 2.3% of all bladder malignancies encountered in surgical specimens. Herein, we describe an adenocarcinoma deeply infiltrating the bladder wall, with no morphologic features of transitional cell carcinoma, in a patient with a previous diagnosis of primary lung adenocarcinoma, mixed subtype. In this case, the use of a limited immunohistochemical panel including napsin A, a recently described highly sensitive marker for lung adenocarcinoma, GATA3 and S100P, two novel markers of urothelial differentiation, was of crucial importance in differentiating between lung adenocarcinoma metastatic to the bladder and primary bladder adenocarcinoma.