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.
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.
