Immunohistochemical Profiling of Metastatic Lymph Nodes to Identify Primary Tumor Sites: A Retrospective Study

Abstract

Introduction: Metastatic lymphadenopathy is a common initial clinical presentation of many malignancies. Immunohistochemistry plays an important role in the determination of the primary site of the tumor. The objective of this study was to analyze the immunohistochemical profile of metastatic lymph nodes and to assess the common primary sites.

Materials and Methods: This was a 4 year retrospective study of all the metastatic lymph nodes analyzed using immunohistochemistry. Regional lymph node excisions done as a part of treatment/staging were excluded from the study. The slides were retrieved and reviewed for morphology and IHC to identify the type of malignancy and the possible primary site. A comprehensive panel of IHC markers were used in most cases selected based on age, sex, clinical and imaging findings and morphology.

Results: A total of 58 metastatic lymph nodes were reported. Cervical lymph nodes including supraclavicular were the most common group of lymph nodes involved in general (97%). A most probable primary site was suggested in 75.8% of cases, lung being the most common site (50%). In a smaller proportion of cases (12%), more than one possible primary was suggested and in 12% a primary site could not be assigned. The most frequently used immunohistochemical marker was CK7(86 %) and TTF1 was the most common site specific marker used (76%).

Conclusion: Immunohistochemistry plays a pivotal role in the work up of metastatic lymph nodes . With an algorithmic approach and judicious use of markers the primary site may be ascertained in most cases, circumventing the need for additional biopsies and other investigations.