Expression of NKX3.1, Prostatic Specific Antigen and Prostatic Specific Alkaline Phosphatase in Cytology Specimens of Metastatic Prostatic Carcinoma

BACKGROUND AND OBJECTIVES: NKX3.1 is an emerging marker for tumors of prostatic origin; however, the utility and diagnostic values of NKX3.1 have not been broadly studied in cytology specimens. The purpose of this study is to determine the performance of NKX3.1, compared to prostatic specific antigen (PSA) and prostatic specific alkaline phosphatase (PSAP), as an organ-specific marker of metastatic prostatic adenocarcinoma (MPAC) in cytology specimens. METHODS: The cytology specimens, which had been evaluated to include or exclude MPAC, were collected from our pathology database. Immunostains for PSA, PSAP, and NKX3.1 were performed on cell block sections. RESULTS: A total of 118 cases were collected. In 37 MPACs, NKX3.1 was diffusely positive in 34 cases (92%) and focally positive in 3 cases (8%). PSA indicated diffuse positivity in 16 cases (43%), focal positivity in 13 (35%) cases, and was negative in 8 (22%) cases. PSAP immunostain was performed in only 12 MPACs, showing diffuse positivity in 5 (42%), focal positivity in 3 (25%), and negativity in 4 (33%) cases. Among the 81 non-metastatic prostatic adenocarcinoma cases, NKX3.1 was negative in 80 (99%) cases and focally positive in only 1 (1%) case; all cases with available PSA and PSAP staining were negative. The calculated sensitivities for NKX3.1, PSA, and PSAP were 100%, 78%, and 67%, respectively, while the specificities were 99%, 100%, and 100%, respectively. CONCLUSIONS: Compared to PSA and PSAP, NKX3.1 is more reliable as an individual marker for MPAC in cytology specimens. Combining NKX3.1 and PSA can be useful in some cases to enhance diagnostic utility.