Clinicopathologic analysis of 66 Japanese thin melanomas with metastasis of sentinel or regional lymph node

Assessment of sentinel lymph node status is commonly performed in the treatment of cutaneous melanoma. However, there are no definite guidelines for thin melanomas with Breslow tumor thickness <1.0 mm, in part because thin melanomas are relatively infrequently positive for lymph node metastasis.

We analyzed the clinicopathologic relationship among tumor thickness, mitotic index, tumor infiltrating lymphocytes (TIL), tumor size, regional lymph node metastasis and prognosis in 66 Japanese patients with thin melanomas. Immunohistochemical evaluations for TIL were also performed.

Thirty-one of the 66 melanomas were Clark level I without lymph node metastasis (0/31, 0%). In tumors of Clark level II or higher (35/66), there were five (14%) regional lymph node metastasis. Melanomas with two or more mitoses in 1 mm(2) per high-power fields showed higher frequencies of lymph node metastasis (2/3, 67%), compared to those with fewer than two mitoses (3/32, 9%). Tumors with intensive TIL that partially or completely surrounded the tumor revealed higher frequencies of lymph node metastasis (5/28, 18%), compared to those with none or slight TIL (0/7, 0%). The main components of TIL were CD8-positive T lymphocytes. No metastasized tumors were under 2.0 cm(2) .

The presence of mitotic activity, large tumor size and an intense lymphocytic infiltrate should prompt sentinel lymph node biopsy in thin melanomas.