Lentigo maligna and lentigo maligna melanoma: a clinicopathologic analysis of twenty-four cases

Abstract

Objective: To study the clinicopathologic features, differential diagnosis and prognosis of lentigo maligna (LM) and lentigo maligna melanoma (LMM). Methods: Histopathologic evaluation and immunohistochemical study by HRP multimer method were carried out in 24 cases of LM and LMM from 2012 to 2017 at Fudan University Shanghai Cancer Center. The clinical information and follow-up data were analyzed. Results: Of total 24 cases, there were 7 cases of LM and 17 cases of LMM; 10 males and 14 females. The age of patients ranged from 32 to 88 years (mean 67 years). The male-to-female ratio was 1.0∶1.4. Tumors were all located on head and face. Clinically, all patients presented with mottled light brown or sepia macule located on head and face for a long time, and some of them followed by nodules or ulceration within the lesion. The diameter of lesions ranged from 0.5 to 3.0 cm. Microscopically, LM and in-situ component of LMM were all characterized by a predominantly junctional proliferation of atypical melanocytes with marked pleomorphism, frequently extending down the walls of hair follicles and sweat ducts. Multinucleate cells were frequently present. The invasive components of LMM mainly consisted of atypical melanocytic spindle cells (13 cases, 76.5%), and the mean Breslow thickness was 1.2 mm (0.1-2.7 mm). The lesions of LM/LMM were generally associated with severe actinic damage, scattered infiltration of lymphocytes and melanophages. Statistically, the number of cases whose diameter of lesion ≥0.6 cm, mitotic rates ≥4/mm(2) and nests of melanocytes within epidermis in group of LMM were significantly more than those in group of LM. Immunohistochemically, atypical melanocytes in LM and LMM were generally positive for S-100, HMB45, PNL2, Melan A and SOX-10. Follow-up was available in all cases, ranging from 1 to 64 months. Only one out of 23 patients with wide surgical excision had local recurrence, and the remaining 22 patients were all alive with no evidence of disease. One LM patient who was merely treated with biopsy was alive with disease progression after 20 months follow-up. Conclusions: LM/LMM is a special subtype of melanoma predominantly located on the sun-exposed skin of elderly people. Recognition of its specific histologic features can help distinguish with sun-damaged diseases and other subtypes of melanoma. The prognosis of LM/LMM patients treated with surgical excision is considered relatively favorable. However, long term follow-up should be recommended in patients with LM/LMM because of high recurrence rates indicated by previous studies.