Other Skin Tumours

RARER SKIN TUMOURS

These are tumours that you should just be able to recognise looking at a slide.  The first one is Dermatofibrosarcoma Protuberans.  These lesions are slow growing nodules that may occur at the site of trauma.  They rarely metastasise and generally just grow locally.  They often extend some distance beyond what is clinically apparent.  The lesions presents as a dermal tumour as a nodule.  There are usually uniform small spindle cells with plump nuclei and may be arranged in what is called a storiform pattern.  They can infiltrate fat in a honeycomb pattern.  There is usually thinning of the overlying epidermal rete ridges and you may get layers of fibrous tissue in the fat, that range parallel to the overlying epidermis.  A pigmented variant of DFSP is the Bednar tumour. In this the dendritic cells contain melanin and it may stain with S100.  It particularly occurs in young women on the trunk and has never been known to metastasise.  The melanin is probably due to colonisation of the DFSO bland melanocytes.

Atypical fibroxanthoma. 

This is a superficial form of pleomorphic undifferentiated sarcoma, previously known as malignant fibrous histiocytoma.  It is a lesion that is particular seen in the elderly and often presents as a pink or purple smooth rapidly growning lesion.  It can resemble an undifferentiated squamous cell skin cancer.  Histologically it is well circumscribed and is found mainly in the upper dermis as a highly cellular tumour.  There is a mixture of three cell types;  spindle shaped cells, large polyhedral cells and multi nuclear giant cells.  An undifferentiated pleomorphic sarcoma is much deeper and has much more a typicality of the cells.  The cells in an AFX look quite abnormal anyway and this is often the most readily recognisable feature.  These lesions only have a small risk of metastasis and it is not as aggressive as its atypia would suggest.  This tumour often has to be excluded from other spindle cell tumours such as the spindle cell squamous cell carcinoma or melanoma.  Melanomas are usually S100 positive. The squamous cell carcinoma is usually pan keratin positive and CD10 positive.  An AFX usually stains for vimentin and is strongly positive for CD10.

Merkel cell carcinoma.

This tumour again is rapidly growing, often smooth dome shaped, varying in colour from red to purple occurring in the sun exposed areas of the head, neck and extremities.  It may be associated with the polyoma virus. When you look at the histology it is one of the blue tumours, in other words blue cells in the dermis, typically these are either lyphmocytomas, lymphomas, basal cell carcinomas, mastocytomas or Merkel cell carcinoma.  Also a small cell metastasis of the lung can look similar.  The cells are round or oval shape with a uniform size and sometimes a vesicular nucleus. Mitoses are common. 

Special immune stains are often necessary to make the diagnosis with certainty.  CK20 is positive while Merkel cell is negative for S100 and thyroid transcription factor.

Microcystic adnexal carcinoma

This is an unusual tumour usually seen on the face, particularly in the upper lip skin and nasal labial fold area.  It presents as a firm plaque or nodule and is very slow growing, but the lesion extends further than you think it does clinically.  Dermatoscopically there may be a lot of milia in the lesion and it looks like a trichoepithelioma and it may be misdiagnosed as such.  Histologically there are strands of squamous and basaloid epithelium with varying duct formation and cysts are common.  Perineural invasion occurs and this lesion seems to get worse as it goes deeper and it invades the subcutaneous fat tissue.  There is mild variation in the size and shape of the cysts.  The major differential diagnosis of this lesion is a sclerosing basal cell skin cancer and breast metastasis.  It may also show lymphoid aggregates, perineural extension is common and note the dense pink to red sclerotic stroma. 

Glomus tumour

These lesions typically occur under the nail with a painful purple discolouration occurring on the nail bed, but they can also occur as solitary lesions elsewhere on the body.  They are tumours of cells that control arterial venous anastomoses and basically are smooth muscle tumours.  Histologically it is a well circumscribed and possibly encapsulated dermal tumour with just a few blood vessels surrounded by sheets of the glomus cells.  These cells are quite round with round nuclei and sometimes eosinophilic cytoplasm.  There is no variation in the cell size or shape. They are often described as being very monotonous.  In a glomangioma usually you will get one or two layers of glomus cells around prominent vessels and usually glomangiomas are multiple.  These vessels have thicker walls and they are probably a vascular malformation with a few glomus cells rather than glomus tumours which are actual tumours of glomus cells.

Angiosarcoma

This tumour usually presents as a bruise like lesion on the head and neck of an elderly patient that is slowly growing.  It can also present as a complication of chronic lymphedema on the legs.  Histologically there are numerous blood vessels that are poorly demarcated.  There are sometimes projections into the lumina and occasionally slit like spaces as much as you would see in a Kaposi's sarcoma.  The endothelial cells are sometimes spindled or epitheliod and atypical and can vary between being mildly atypical to markedly atypical.  There are often extravasated erythrocytes with hemosiderin staining and positive staining with endothelial cell markers such as CD31 or CD34.

 Kaposi's sarcoma

This used to be a rare vascular tumour seen in elderly Jewish males in Eastern Europe but with the advent of aids it became much commoner in a younger population.  It is now known to be associated with the Herpes 8 virus and is a feature of early HIV and aids.  It can present as bruise like macules or as papules and nodules, usually a purple colour, typically on the face and sometimes orally as well.  It is essentially a vascular proliferation response to the Herpes 8 virus rather than a true sarcoma and it may begin in multiple areas at once.  Typically histologically the dermis has slit like vascular spaces lined by spindled endothelial cells.  Older lesions can have solid areas of spindle cells.  Cellular atypia is usually mild but again there are often extravasated erythrocytes.  Immuno staining for Herpes virus 8 is usually positive.  The two major differentials are acroangiodermatitis, sometimes known a pseudo Kaposi's related to stasis.  This condition may have some spongiosis and mature vessels and less of the slits.  Secondly a pyogenic  granuloma has a more rapid onset and more inflammation but again fewer slit like spaces.

Angiolymphoid Hyperplasia with Eosinophilia

This condition usually presents with nodular lesions on the head and neck that are a red or purple colour.  Histologically there are thick walled vessels with hobnail endothelium and there may be nodular lymphoid aggregates but with eosinophils.  A similar condition is Kimura's  disease but it lacks the thick walled vessels with the hobnail endothelium.  It does have deep lymphoid nodules with eosinophils and has peripheral eosinophilia and elevated IgE.  In Kimura's the prominent lymphoid follicles often have germinal centres and are a bit deeper but otherwise the pathology is similar to angiolymphoid hyperplasia with eosinophilia.

Mastocytosis

Here you may have many blue cells in the dermis depending on the thickness of the lesion and they are very uniform cells, sometimes described as being fried egg like.  In the condition TMPE there is a much more subtle increase of spindle shaped mast cells around blood vessels.  Solitary mastocytomas occur in children and just spontaneously involute and are rarely biopsied.  In urticaria pigmentosa there is often some basal layer hyperpigmentation corresponding to the red/brown lesions seen in the skin surface and the mast cells are congregated around the blood vessels of papillary dermis.  It is said that the presence of more than five perivascular mast cells around a papillary dermal vessel is suggestive of mastocytosis.  Special stains may be needed to show up the mast cells including Toluidine blue and Giemsa.  Sometimes the mast cells are cuboidal and may resemble naevus cells, but mastocytomas don't show junctional or lower dermal nesting.

Granular cell tumours

These lesions are rare, they typically occur on the tongue but they can be seen in a solitary nodule on the extremities.  Usually the diagnosis is made histologically because there are sheets of large polygonal cells with an eosinophilic granular cytoplasm and a central nucleus.  The overlying epidermis may show pseudo epitheliomatous as hyperplasia.  The lesion is S100 positive.

Granular cell tumours are derived from Schwann cells and the granules within them are phagolysosomes. They look fairly bland but should be excised with at least 5mm margins and they should be regarded as potentially malignant.

Leiomyoma

Leiomyoma is a benign smooth muscle tumour.  Usually derived from the arrector pili muscles or from the walls of the blood vessels.  They are sometimes also seen in genital skin derived from the dartos muscle.  They are sometimes given the name of piloleiomyoma derived from a follicle muscle.  Angioleiomyomas are from the smooth muscle of the blood vessel and leiomyoma from the genital skin.  Smooth muscle cells have cigar shaped nuclei with blunt ends.  Piloleiomyomas derived from the arrector pili muscles may present as multiple red/brown lesions.  They sometimes adopt a linear pattern. They can be locally painful and can respond to cold with pain. Rarely multiple lesions have been associated with uterine leiomyoma and sometimes renal carcinoma.  Angioleiomyomas typically occur in the lower leg of adults.  Most are painful.  Leiomyoma sarcomas are the malignant equivalent of a leiomyoma. Again they are usually in men on the lower legs, on the extensor surfaces.  Local recurrence is common but metastasis is rare.  Again there is intertwined fascicles of fusiform cells with blunt cigar shaped nuclei and an eosinophilic cytoplasm.  There may be an increased number of mitotic figures and certainly they are more pleiomorphic than in a leiomyoma.