Case 14 Female, 55 years. Skin lesion, dorsum of footShow diagnosis & comments
Superficial spreading melanoma, variable cell types; small cell basal component ('pseudomaturation')
Not uncommonly, melanoma cells at the base of melanoma are smaller than superficial ones. They can be identified as an integral part of the melanoma, because they are stll atypical, and often cluster in irregular compact nests or small cell groups. Mitotic figures are sometimes identified. Transitions from larger to smaller cells are ofte abrupt, and within the basal part of the melanoma there is often consifderable variability in architecture and cellular features.
Small melanoma cells at the base can lead to a minor and a major diagnostic mistake. The minor one would be to regard this part of the lesion as a naevus remnant, resulting in a lower outcome of the Breslow thickness measurement. The major mistake is to regard the presence of small cells at the base as an indication of maturation of the entire lesion, and missing the diagnosis of melanoma.
Presence of smaller melanoma cells at the deepest part of the melanoma is sometimes referred to by the ugly but reasonably self-explanatory term 'pseudo-maturation'.