**5. Histopathological analysis**

The presence of nodal micrometastases (0.2 mm–2 mm) or isolated tumour cells (ITC) (<0.2 mm) [9] may be overlooked by standard histopathological analysis, with one study that reanalysed 76 neck dissection specimens with serial sectioning identifying previously undetected micrometastases in 7.9% of specimens [25]. These metastases occurred mainly in small (<1 cm) lymph nodes, without extranodal extension and therefore would not have been routinely identified on preoperative imaging. **Figure 6** demonstrates how micrometastases are detected more reliably by performing serial sectioning. Another smaller prospective study analysed 34 neck dissection specimens with serial sectioning and immunohistochemistry (IHC) in addition to standard haematoxylin–eosin staining (HES) and found that 3 patients (8.8%) were upstaged by the additional analysis, with two cases of micrometastases and one patient harbouring ITC [26]. Importantly the identification of these micrometastases did not warrant further treatment beyond the neck dissection which had already been performed [25]. However, the revised findings of node positivity has both a staging and prognostic impact on patients.

In another study in the setting of SLNB, serial sectioning and IHC upstaged 5 of 27 (19%) patients with nodal metastases [8], and a retrospective review of 272

**Figure 6.** *Serial sectioning a lymph node.*

#### *Sentinel Lymph Node Biopsy for Early Oral Cavity Squamous Cell Carcinoma DOI: http://dx.doi.org/10.5772/intechopen.99410*

patients undergoing SLNB found that 51.7% of their positive sentinel lymph nodes were only detected following serial sectioning and IHC [27]. The addition of IHC to standard HES increases both the sensitivity and negative predictive value of SLNB [16, 28, 29] and has now become part of the standard pathological assessment of SLNs in most institutions.

Performing serial sectioning and IHC (cytokeratin – AE1/AE3) is both labour and time intensive for the pathologist. By performing a SLNB, the detailed examination can be focused on the most likely lymph nodes which might harbour micrometastatic disease for each individual patient, providing the most precise staging and prognostic information.
