Adenocarcinoma with Unknown Primary: Diagnostic Implications using Immunohistochemistry
Carcinoma of unknown primary site (CUP) is a heterogeneous group of cancers defined by the presence of metastatic disease with no identifiable primary tumor at presentation. We undertook this study to assess the utility of immunohistochemistry (IHC) for the determination of primary tumor site in adenocarcinomas. This retrospective study included 51 cases with a morphological diagnosis of metastatic adenocarcinoma with unknown primary. Basic IHC panel that included cytokeratin 7 (CK-7), cytokeratin 20 (CK-20), pan-cytokeratin (pan-CK), thyroid transcription factor-1 (TTF-1), and caudal type homebox 2 (CDX-2) was used. Additional extended panel with specific IHC markers was used in cases where the primary could not be determined using the basic panel. The male-to-female ratio was 1.4:1 with mean age of 50 years. The most common metastatic site was lymph node followed by liver. A conclusive diagnosis using IHC was achieved in 30 cases (58.82%). Specific diagnosis could be made in 8 cases (16%) using basic IHC panel. Extended panel yielded specific diagnosis in additional 22 cases (43.13%). Primary site could not be determined using even both the panels in 21 cases (41.18%). The panels for identification of the primary need to be flexible depending on the site of metastasis, age/sex of the patient, and detailed history, which may determine sensitivity and specificity of primary detection.