The Clinical Significance of Tumor-Infiltrating Lymphocytes and Microscopic Satellites in Acral Melanoma in a Korean Population

BACKGROUND: There are various histological prognostic parameters of cutaneous malignant melanoma, including tumor thickness and ulceration. Tumor-infiltrating lymphocytes (TIL) are among these parameters and can be further classified into three categories: 'absent', 'non-brisk' and 'brisk'. Brisk TIL usually indicates better clinical prognosis. Microscopic satellite (Ms) is defined as a nest of tumor cells that is greater than 0.05 mm in diameter and definitely separated from the main tumor. Even though the incidence of Ms varies according to Breslow thickness, the presence of Ms generally indicates poor prognosis. OBJECTIVE: Clinical significance of both TIL and Ms has been extensively studied in western populations but much less so in Asian countries, including Korea, where acral melanoma is the most common subtype. METHODS: We reviewed 90 patients with acral melanoma diagnosed at Kyungpook National University Hospital in Korea. Tissue specimens were examined using hematoxylin-eosin and HMB45 immunohistochemical staining. They were also evaluated by the presence and categorization of TIL (absent, non-brisk and brisk) and the presence of Ms. We further evaluated their impact on survival events (recurrence, distant metastasis and death). RESULTS: The number of survival events by TIL type was 22 in the absent category (22/64, 34.4%), 3 in the non-brisk category (3/25, 12.0%) and 0 in the brisk category. For Ms, survival events were present in 7 patients in Ms-present group (7/11, 63.6%) and 21 patients in Ms-absent group (21/79, 26.6%). CONCLUSION: We suggest the possibility of TIL and Ms as prognostic indicators for acral melanoma in Korean population.