Is lymph node biopsy important in thin melanoma?

This study investigated which characteristics of thin melanomas are associated with positive lymph nodes (melanoma spread to the lymph nodes) and the outcomes of these patients.

Melanoma is a type of skin cancer that originates in the pigmented cells of the skin (melanocytes). If these tumors are caught early, when they are 1 mm or less thick (thin melanoma), surgical removal often results in a cure for the patient. Due to raised awareness of skin cancer, the number of patients diagnosed with thin melanomas is high. The first place a melanoma spreads to is the nearby lymph node basin. However, checking for lymph nodes-spread melanoma through biopsy (a tissue sample examined under a microscope) in thin melanomas is controversial, because in very few cases thin melanoma is associated with positive lymph nodes. This study aimed to evaluate whether there are specific features of a thin melanoma associated with positive lymph nodes.

189 patients with early stage/thin melanomas (tumor of 1 mm or less thick) were included in this study. All participants had biopsies taken from the nearest lymph nodes and underwent surgery to remove the melanoma. A pathologist evaluated the microscopic features of the melanoma such as the location of the tumor, the number of dividing cancer cells (mitotic rate), presence of microscopic ulceration (small breaking of the skin over the melanoma seen only under a microscope), and depth of the melanoma. These features were associated then with the presence or absence of positive cancer cells at the lymph node biopsy and patients’ survival. 

After approximately 40 months of follow up, there were no significant differences in any features of the melanoma between patients with positive and negative lymph nodes. Only 3 patients out of 189 (1.6%) had positive lymph nodes at the biopsy, 2 of them had progressive disease and later developed distant metastases (cancer spread to distant organs of the body) and 1 had died. There was no association between any other characteristics of the melanoma and survival. While the mitotic rate was not associated with positive lymph nodes, a mitotic rate greater than 3 mitoses per square millimeter was linked to a poorer prognosis.

Overall, this study showed that although lymph nodes are positive in only a small number of patients with thin melanoma, this is linked to a higher likelihood of the cancer spreading. Also, there were no specific microscopic features of the tumor that could predict lymph node involvement in these patients.

The number of patients with spread melanoma was very small, which makes it difficult to draw a clear conclusion. Also, the follow up period was relatively small. Further studies on larger populations of patients and on bigger periods of time are warranted to confirm these results.