Clinical Significance of Sentinel Lymph node in melanoma:
SLNB is very accurate in predicting the status of the remaining regional lymph nodes. It is currently the most significant independent prognostic indicator for survival when compared with all other factors, including tumour thickness and the presence of ulceration.
According to some studies, the relapse rate for H&E detected SLN positive patients is higher (up to 67%), whereas the relapse rate for SLN negative patients is low (2–6%) during the same period.
Indications for SLNB procedure :
Primary Melanoma with thickness greater than 1.0 mm or
Primary Melanoma less than 1mm with Clark's level IV or V or presence of ulceration.
The current standard for the diagnosis of SLN metastasis is based on routine H&E histology and immunohistochemistry (IHC). I follow the Cochran Method.It is as follows: 1. The lymph node is either bivalved or cut into 3 mm blocks, depending on the size of the node. 2. Sections 1, 3, and 5 are stained with haematoxylin and eosin (H&E); 3. Sections 2 and 4 are immunohistochemically stained for S-100 and HMB-45
The sensitivity of detection is increased with IHC, multiple sectioning and reverse transcriptase polymerase chain reaction (RT-PCR) techniques. The role of such molecular genetic techniques in identifying melanoma proteins remains undefined, despite greater sensitivity.
Caution: ‘‘Surgeons should be aware that the subcapsular region is crucial in sentinel lymph node (SLN) evaluation and the architecture of the SLN can be disrupted easily if the procedure is not carried out with care’’
To reduce the false negative rate, surgeons should avoid crushing and excessive cautery usage to preserve the integrity of the SLN. It is also important not to cut into the SLN and complete excision of the whole SLN is crucial.
False positive results: False positives resulting from
Benign naevic cells raise concern and necessitate further refinement. Naevic cells are usually present within the capsule (intracapsular) or within the trabeculae, and typically stain negatively, or only faintly positively, with HMB-45.
Reactive dendritic cells, nerve fragments, and benign naevic cells may each stain positively for S100.HMB-45 stain allowed us to differentiate benign naevic cells from their malignant counterparts. Examination at the subcapsular level, combined with the use of S100 staining, is the most practical and sensitive method to ensure the detection of micrometastatic nodal disease.