D: Skin Malignancy

Skin malignancy most commonly arises from the keratinocytes of the epidermis. Other cell types can also cause cancer, such as melanocytes or Merkel cells.

Cancer types

Basal Cell Carcinoma

The most common malignancy of humans; the incidence is hard to estimate as it is usually not considered a reportable cancer. It typically occurs in sun exposed skin; other aetiological factors include immunosuppression and familial germline mutations (eg. Gorlin syndrome). A number of basal cell carcinomas show mutations in the Sonic Hedgehog Pathway, usually in the PTCH1 gene; this allows unrestricted activity of SMO1 which promotes the usual suspects. Common features among the basal cell carcinoma subtypes are small basaloid cells with scant cytoplasm with a loose fibromyxoid stroma. There are several subtypes:

  • Nodular BCC (60-80%): Cells are arranged in lobules or nests with peripheral palisading with some mitotic activity. The lobules are separated by fibromyxoid stroma.
  • Superficial BCC (10%): Cells extend into the dermis from the epidermis. There is often a cleft seen on histopathology between the malignancy and the dermis. There is peripheral pallisading along the tumour border.
  • Micronodular BCC (5-10%): Cells are arranged in small nodules with a collagenous stroma. They often extend outside of the macroscopic lesion.
  • Infiltrative BCC (5%): Cells are arranged in cords and strands instead of nodules, and often spread beyond the macroscopic lesion which is often pale and slightly raised.
  • Morphaeic BCC (< 5%): Shares the appearance of the infiltrative type but with a sclerotic stroma.

Immunohistochemistry is negative for S100 and positive for keratin; cytokeratin 20 is usually absent in contrast to Merkel Cell Carcinoma where it is positive.

Squamous Cell Carcinoma


Merkel Cell Carcinoma

Sarcoma of the Skin

Lymphoma of the Skin

Adnexal Tumours

Benign Tumours of the Skin