Basal cell carcinomas, squamous cell carcinomas and melanomas account for close to 98% of all skin cancers. They are all related to UVR, and the incidence of all these cancers have increased markedly over the last two to three decades.

A range of other tumours account for the remaining 2%, and although we expect you have to heard of them, we do not expect you to know much about them. Many of these tumours are hard to diagnose clinically, and their management based on ‘reason’ and anecdote rather than robust empirical study. Some of these tumours, such as Merkel cell carcinomas and some appendage tumours appear UVR related — and their rates have increasing over recent decades. Others, such as skin sarcomas and cutaneous B cell and T cell lymphomas do not appear related to UVR.

Merkel cell carcinoma (MCC)

This is a neuroendocrine carcinoma of skin. It is rare, but only has a 70% survival rate at 5 years (due to metastatic spread). It is believed that the Merkel Cell Polyomavirus is causally implicated in its pathogenesis. Not surprisingly, MCC rates are raised in the immunosuppressed. It is treated by excision with or without radiotherapy. The bigger the primary tumour the worse the prognosis. An image of a typical MCC is shown below.

Appendageal carcinomas

There are a large number of benign keratinocyte tumours related to hair follicles and sweat glands: do not delve deeper. There are occasional malignant tumours of these structures that are often managed as thought they were squamous cell carcinomas. Many are capable of metastasis. Below is an image of a malignant sweat gland tumour.

Cutaneous lymphoma

There are primary lymphomas of the skin, which can be T cell or B cell. Cutaneous T cell lymphoma (CTCL) usually presents as a widespread rash that resembles psoriasis, and is often misdiagnosed as psoriasis. Cutaneous B cell lymphoma (CBCL) usually presents as erythematous nodules or plaques. The clinical behaviour and classification is very varied and management requires close collaboration between dermatologists and haematologists. Some images of B cell lymphoma are shown below.


The most common primary cutaneous sarcoma is the dermatofibrosarcoma protuberans (DFSP). It often presents as a firm nodule or plaque reminiscent of an ‘odd’ dermatofibroma, over the shoulder girdle in a young adult. Treatment is by wide excision with or without therapy. Local recurrence is common and metastatic spread my occur in a minority of cases.

An image of another type of cutaneous sarcoma, a leiomyosarcoma, is shown below. Again, it presented as a firm indolent nodule with diagnosis relies on clinical suspicion and histopathology.

Kaposi Sarcoma (KS)

This is a spindle cell malignancy derived from vascular endothelium. It occurs in various patient groups, including untreated HIV/AIDAS infections, other immunosuppressed groups (e.g organ transplants), and some elderly populations. The Human Herpesvirus 8 (KS associated herpesvirus) is implicated in all cases. The image below is from a HIV infected person. The clinical presentation is highly variable.

(Image by  OpenStax College – Anatomy & Physiology, Connexions Web site., Jun 19, 2013., CC BY 3.0, Link)

Cutaneous secondaries

Metastatic deposits from internal malignancies are rare. The image below is a secondary adenocarcinoma in the umbilicus (‘Sister Mary Joseph nodule’) [ ]

Cutraneous metastases from primary skin cancers are most commonly see in melanoma (see image below).

Skincancer909 by Jonathan Rees is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Where different rights apply for any figures, this is indicated  in the text.