M 77, right upper arm, 1.2 cm nodule

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Diagnosis:
Hidradenoma, solid-cystic type (Eccrine adenoma, solid and cystic type)
Comment:

Clinical:

Location: mostly head and neck, limbs, or any site.
Middle age and elderly, F>M.
Solitary, slow-growing solid or cystic dermal nodule, 1-2 cm.

Pathology:

Well circumscribed, un-encapsulated solid and cystic lobular dermal tumor, 50% connected to the epidermis.
Biphasic cellular pattern: areas of round, fusiform, polygonal squamoid cells with eosinophilic cytoplasm and cells with clear cytoplasm.
Duct-like structures, cystic change, focal apocrine change, squamous eddies, goblet cells  etc may be present.
Stroma is fibrovascular, collagenous or hyalinized.
Tumor ‘budding’ from the periphery to the surrounding dermis should be considered as a low-grade malignant tumor.
Diffuse nuclear anaplasia, necrosis and tumor giant cells may suggest malignancy.