Histopathologic review of negative sentinel lymph node biopsies in thin melanomas: an argument for the routine use of immunohistochemistry

Sentinel lymph node assessment in melanoma: current state and future directions

Assessment of sentinel lymph node status is an important step in the evaluation of patients with melanoma for both prognosis and therapeutic management. Pathologists have an important role in this evaluation. The methodologies have varied over time, from the evaluation of dimensions of metastatic burden to determination of the location of the tumour deposits within the lymph node to precise cell counting. However, no single method of sentinel lymph node tumour burden measurement can currently be used as a sole independent predictor of prognosis. The management approach to sentinel lymph node-positive patients has also evolved over time, with a more conservative approach recently recognised for selected cases. This review gives an overview of past and current status in the field with a glimpse into future directions based on prior experiences and clinical trials.

PRAME expression in 155 cases of metastatic melanoma

BACKGROUND

PRAME (preferentially expressed antigen in melanoma) is a promising immunohistochemical marker in distinguishing benign from malignant primary cutaneous melanocytic lesions and lymph node deposits. We hypothesize that PRAME may also reliably identify melanoma metastases that are clinically detected in skin, lymph nodes, or small intestine.

METHODS

A total of 155 cases of metastatic melanoma to lymph node (N = 54) and non-lymph node (N = 101) sites were stained with an antibody against PRAME. Nuclear expression was scored in tumor cells as negative, 1% to 25% (1+), 26% to 50% (2+), 51% to 75% (3+), or 76% to 100% (4+).

RESULTS

PRAME expression was seen in 151/155 (97.4%) cases, with 4+ expression in 64 cases (41.3%), 3+ expression in 46 cases (29.7%), 2+ expression in 18 cases (11.6%), and 1+ expression in 23 cases (14.8%). Lymph node metastases were more likely to show lower expression as compared to metastases to other anatomic sites (P = 0.003).

CONCLUSIONS

A high level of PRAME immunoreactivity was identified in this cohort of metastatic melanoma. Lymph node metastases showed more focal or absent PRAME expression as compared to metastases to other sites. Overall, PRAME is a useful tool for confirming the diagnosis of melanoma in a metastatic setting, in both nodal and visceral deposits.