Male, 54 years. Diffuse swelling and induration, skin of foreheadShow diagnosis & comments
- Usually arises in chronically sun-damaged skin
- Nondescript papule, plaque or more diffuse induration and thickening of the skin
- Punch biopsy diagnosis requires a high level of suspicion (S-100 immune stain is mandatory and usually clinches the diagnosis).
- Nonpigmented proliferation of elongated atypical cells within the dermis, associated with newly formed collagen
- Mitotic figures usually uncommon
- Enlarged hyperchromatic elongated nuclei, often with coarse chromatin and plump nucleoli
- No melanin pigment
- Cells lie singly or in small elongated cell groups
- S-100 stain strongly positive (see panels of micrographs of immune stain, which is S-100), most other melanocyte markers such as Melan-A and HMB-45 negative.
- Perivascular round cell inflammatory infiltrates
- There may or may not be an intraepithelial atypical melanocytic proliferation
- Peri- or intraneural growth resulting in increased likelihood of local recurrence
- Metastasis is rare in pure demoplastic melanomas; not rare when the melanoma also shows a non-desmoplastic component
- The tumour cells of desmoplastic melanoma are strongly S-100 positive, but negative for Melan-A (MART-1), HMB-45 (gp100), usually MITF and tyrosinase. Therefore, an S-100 immunostain is extremely important diagnostically. In any case where a skin biopsy reveals an increased number of enlarged elongated cells within the dermis, and especially when derived from sun-damaged skin and when perivascular round cell infiltrates are present, an S-100 stain is mandatory.
- In scar tissue, there may be small numbers of elongated, slender, S-100 positive cells, which should be borne in mind in order to avoid overdiagnosis of this rare melanoma variant.
- Busam KJ. Desmoplastic melanoma. Clin Lab Med. 2011;31(2):321-30.Busam KJ. Cutaneous desmoplastic melanoma. Adv Anat Pathol. 2005;12(2):92-102.
- Busam KJ, Mujumdar U, Hummer AJ, Nobrega J, Hawkins WG, Coit DG, Brady MS. Cutaneous desmoplastic melanoma: reappraisal of morphologic heterogeneity and prognostic factors. Am J Surg Pathol. 2004;28(11):1518-25.
- Robson A, Allen P, Hollowood K. S100 expression in cutaneous scars: a potential diagnostic pitfall in the diagnosis of desmoplastic melanoma. Histopathology. 2001 Feb;38(2):135-40.