Case Number : Case 1830 - 2 June - Dr Richard A Carr Posted By: Guest

Catchup Time... a great case from Dr Richard A Carr

Geoff Cross - DermpathPRO Projects

Looks like a recurrent nevus, but there’s an atypical deep dermal component and atypia seems exorbitant...so I go with Melanoma ( partially regressed ).  

Favor recurrent nevus until review of the original biopsy specimen, if available, proves otherwise.

Agree, had the same differential. Difficult case just based on this morphology. CPC needed

Difficult, favor regressing melanoma

Agree. Melanoma with regression versus persistent/recurrent nevus. Favor melanoma as in the non-fibrosed area the lesion shows considerable architectural atypia. An elastic stain may also help in differential diagnosis. In regressed lesion clumping of elastic fibrous is usually seen at the base of the biopsy. 

70yo, male, back, history of previuos ressection not informed. Epidermal atrophy, epidermal consumption, irregular nests, pagetoid cells, wide lentiginous component, fibroplasia, atypical cells, linfocitary infiltrate. I go --> melanoma.

Apologies for the late post (entirely my fault). I think on the images here you have all done well. I think this is actually a good example of the small cell malignant melanoma, a variant of naevoid melanoma. Some years ago I submitted it to a national and international melanocytic slide club which I organise and amazingly there was 90% agreement for the diagnosis of melanoma although clearly the differential does include traumatised naevus. Continuation of the atypical lentiginous process, fairly typical for "in situ" melanoma, into the areas of preserved rete and growth down the sweat duct are helpful clues. These lesions are invariably radial growth phase (lacking dermal mitotic activity) and complete excision should be curative.

Reference: Blessing et al J Clin Pathol 2000, 53(8):591-595.

Incidentally I don't think there is any significant pagetoid spread of the atypical melanocytes here. Just perinuclear vacuoles around the keratinocytes in the epidermis. Be careful to look for the rim of cytoplasm around true pagetoid melanocytes. The confluent, mildly atypical lentiginous proliferation is quite sufficient for a melanoma in situ component in this clinical context.