Case Number : Case 847 - 16th September Posted By: Guest

Very broad junctional melanocytic lesion on sun damaged skin, highlighted by Mart-1. There is some brown stuff in the papillary dermis, but from low magnification I guess they are melanophages. Since Mart-1 often picks up activated keratinocytes too, I prefer to use it in conjunction with MiTF to better characterize the pagetoid spread and confluent proliferation of melanocytes. This is certainly early melanoma in situ, lentigo maligna type.

I favor lentigo simplex.

Although there is marked solar elastosis, the junctional melanocytes appear cytologically bland (no enlargement, pleomorphism, hyperchromatism, angulated nuclear/cytoplasmic contours, or 'starburst' multinucleated giant cells). No significant architectural atypia is present (neither high level intraepidermal pagetoid scatter, nor downward pagetoid spread along eccrine or follicular adnexa on Melan-A immunostain; there is no lentiginous confluence, and no irregular junctional nesting at least in the images provided). This biopsy shows heavy melanin in basal keratinocytes and in stratum corneum, which I imagine might clinically correspond with an 'inkspot lentigo' or dark macule.

De novo lentiginous melanocytic proliferation in sun damaged skin, adult patient. Of course melanoma in situ goes on top of differential although I share the doubts of dr Davie,and I am not able to dispell matter on the posted images. Unfortunately, Melan A may not be always helpful in these circumstances inasmuch as it is often picked up by keratinocytes, either single or in nests hence the word of caution by Graz people (AJD: 2004 Oct;26(5):364-6; AJD 2009 May;31(3):305-8) to use it in combination with other markers including HMB45 and S100 protein.

I find the use of Giemsa counterstain (in place of hematoxylin counterstain) invaluable when using DAB (brown chromogen) immunohistochemistry on pigmented lesions; I find it a [b]much [/b]preferred alternative to melanin bleaching.
Melanin granules will stain a distinct dark green-brown, whereas DAB is a pure brown; this makes identification of melanophages and pigmented keratinocytes much easier, and does not suffer the cytology-obscuring, overstaining artefact often seen when using ACE (red) chromogen as an alternative to DAB (brown), which makes it easy to see both melanin granules and positive DAB staining in the same cells. [Not to mention, DAB is more durable than ACE over the years.]