Lipomatous mixed tumour of the skin: a histological, immunohistochemical and ultrastructural study.
BACKGROUND
Mixed tumours are composed of an admixture of an epithelial/myoepithelial and usually a myxochondroid stromal component. Adipocytes are found more rarely, and account for a minor part of the tumour. To date, only three cases of mixed tumour/pleomorphic adenoma of the salivary gland have been described, showing an extensive adipocyte content of more than 90% of the tumour tissue. Owing to this peculiarity, some authors have defined it as 'lipomatous pleomorphic adenoma'. We are not aware of previously reported similar lesions in the skin.


OBJECTIVE
We report a case of a tumour that occurred as a 2 x 2 x 1.5 cm nodule in the scalp of a 65-year-old man. Analogies with salivary lipomatous pleomorphic adenoma, as well as histogenesis and differential diagnoses are discussed here.


METHODS
A histological, immunohistochemical and ultrastructural study was performed.


RESULTS
The tumour was well-circumscribed and showed a substantial mature adipose tissue component intermingled with epithelial cells arranged in ducts and branching tubules, embedded in a fibromyxoid stroma, which was diagnostic of a chondroid syringoma/mixed tumour. Adipocytes strongly expressed S-100 protein and cytokeratin 14. Transitional elements from epithelial/myoepithelial cells into adipocytes were observed. They coexpressed cytokeratin 14, S-100 protein and vimentin, and showed lipid droplets, desmosome-type junctions, cytoplasmic tonofilaments and basal lamina.


CONCLUSIONS
The tumour differed from lipomas with myxoid stroma and from lipoadenomas, which show non-proliferating normal sweat glands admixed with adipose tissue. Because of the similarity to lipomatous pleomorphic adenoma/mixed tumour of salivary glands, we suggest that it should be called 'lipomatous mixed tumour of the skin'.
Miracco
C
C
Institute of Pathological Anatomy and Histology, Policlinico Le Scotte, University of Siena, Viale Bracci 6, 53100 Siena, Italy. miracco@unisi.it
De Santi
M M
MM
Lalinga
A V
AV
Pellegrino
M
M
Schürfeld
K
K
Sbano
P
P
Miracco
F
F
D008949:Adenoma, Pleomorphic / Q000737:chemistry / Q000648:ultrastructure*; D000368:Aged; D006258:Head and Neck Neoplasms / Q000737:chemistry / Q000648:ultrastructure*; D006801:Humans; D008297:Male; D009363:Neoplasm Proteins / Q000032:analysis; D012535:Scalp / Q000737:chemistry / Q000648:ultrastructure*; D012878:Skin Neoplasms / Q000737:chemistry / Q000648:ultrastructure*
D009363:Neoplasm Proteins