Other common and uncommon tumours

Microcystic adnexal carcinoma

This is an unusual tumour usually seen on the face, particularly in the upper lip skin and nasal labial fold area.  Presents as 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.

Granular cell tumours

These lesions are rare, they typically occur on the tongue but they can be seen as 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  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 they are 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 when derived from a hair follicle arrector 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 on the lower leg of adults.  Most are painful.  Leiomyosarcomas are the malignant equivalent of a leiomyoma. Again they are usually seen 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 pleomorphic than in  a leiomyoma.