Detection of cervical lymph node micrometastasis and isolated tumor cells in oral squamous cell carcinoma using immunohistochemistry and serial sectioning

INTRODUCTION Oral squamous cell carcinoma (OSCC) comprises one of the largest subsets of cancers with a tendency for regional metastasis. Nodal status is a key prognostic indicator in patients with OSCC, particularly with N0 neck. Occult metastasis in the form of micrometastasis (MM) and isolated tumor cells (ITCs), often goes undetected by routine hematoxylin and eosin (H&E) examination using 1-2 sections for analysis. This limitation could be overcome by combining serial sectioning (SS) with immunohistochemistry (IHC) for the detection of MM and ITC. Pan-cytokeratin (pan-CK) (AE1/AE3) is particularly a useful marker to detect these deposits as their presence has resulted in varied interpretations and different applications of the tumor-node-metastasis system. OBJECTIVES The objective of the study was to identify a suitable method for detecting MM and ITC in lymph nodes (LNs) of OSCC by combining SS and IHC and to compare it with conventional H&E staining. MATERIALS AND METHODS This laboratory-based, prospective study was conducted on 133 LNs harnessed from ten patients treated with radical neck dissection for primary OSCC. The LNs were subjected to SS at 100 μm intervals. The sections were stained with routine H&E staining, pan-CK and analyzed for MM and ITC according to criteria laid by Hermanek et al. STATISTICAL ANALYSIS The obtained data were subjected to statistical analysis using Chi-square test. RESULTS The application of combination of SS and IHC using pan-CK (AE1/AE3) in our study revealed the presence of MM and ITC in 2.25% of the LNs diagnosed as negative on routine H&E examination. The detection of these occult metastatic deposits resulted in upstaging of 33.33% of the patients. CONCLUSION In the view of crucial role of occult LN metastasis in prognosis and survival of OSCC patients with N0 neck, diagnostic tools such as IHC staining, particularly with pan-CK (AE1/AE3), combined with SS should be preferred over conventional methods as they result in upstaging, thus sparing the low-risk patients the morbidity of unnecessary treatment.