Evaluation of the role of routine melan-A immunohistochemistry for exclusion of microinvasion in 120 cases of lentigo maligna.

To assess the usefulness of routine melan-A immunohistochemistry (IHC) for exclusion of microinvasion in lentigo maligna (LM). One hundred and twenty cases of LM from our archives were reviewed by 2 authors with S100 protein and melan-A IHC using a red chromogen. Melan-A was useful to confirm the diagnosis of LM in early lesions and to differentiate these from chronically sun-damaged skin. The presence of scattered melan-A-positive cells was noted in the dermis in 72 of 120 cases (melanophages in 36 cases, nonspecific cells different to melanophages in 16 cases, and a dual cell population in 20 cases). The significance of these cells was uncertain. Only 3 cases suspicious for microinvasion were identified: 2 on haematoxylin and eosin and 1 on S100. We recommend use of melan-A to confirm the diagnosis in early lesions of LM and in the differential diagnosis from melanocytic hyperplasia in chronically sun-exposed skin. We do not recommend routine use of melan-A to identify or exclude microinvasion. However, it may have a role, in conjunction with S100, in cases with suspicious features for early invasion on haematoxylin and eosin sections.