Cysts:

Hydrocystoma -Eccrine/Apocrine

Hamartomas:

Eccrine/Apocrine naevus

Eccrine Angiomatous Hamartoma

Porokeratotic eccrine ostial naevus

Benign Neoplasms:

Syringocystadenoma Papilliferum

Hidradenoma Papilliferum

Nipple Adenoma

Syringoma

Spiradenoma

Cylindroma

Chondroid Syringoma (benign mixed tumour)

Poroma

Hidradenoma

Apocrine adenoma

Papillary eccrine adenoma

Syringofibroadenoma

Porocarcinoma was first described by Pinkus and Mehergan as 'epidermotropic eccrine carcinoma' and probably represents the commonest form of sweat gland carcinoma.

Some tumours are of long duration suggesting malignant transformation of a poroma or hidroacanthoma simplex . Rarely some may arise from organoid nevus.

Age:  Predilection for older patients  

Site: Usually located on distal extremities.

Clinical presentation: Presents as a verrucous plaque  or polypoid growth.

Microscopic features:

Asymmetrical , infiltrative growth pattern  ;  Large smooth islands and small irregular shaped nests   ;  Focal necrosis (comedonecrosis) ;  2 types of atypical cells: eosinophilic and clear cells. Eosinophilic cells - polyhedral or fusiform with round to oval hyperchromatic nuclei, distinct nucleoli, indistinct cell boundaries, and a variable amount of cytoplasm (small eosinophilic cells or large eosinophilic cells);  Clear cells  -  large and polyhedral with round to oval nuclei, abundant clear cytoplasm, and distinct cell borders ; Clear cell areas are less prominent than hidradenocarcinoma  ; Ductal structures  ;  Intracytoplasmic lumina formation ; Squamous differentiation ; Melanin pigment is demonstrated in some cases ; Tumour shows multiple attachments to the epidermis ; Inflammatory infiltrate around neoplastic masses is composed of lymphocytes and plasma cells, rarely mixed with neutrophils and eosinophils ; Tumour with only intra- epidermal component is known as in-situ porocarcinoma ; Intraepidermal portion of the growth is composed of large atypical cells arranged in irregular nests and islands, variable in size and in shape, and sharply demarcated from the surrounding epidermal keratinocytes.

Benign component of poroma and hidroacanthoma simplex is present in about 10% of cases.

Neoplastic cells contain glycogen and intratubular, PAS-positive, diastase-resistant material is usually present.

Immunocytochemistry:  Tumour is cytokeratin , CEA and epithelial membrane antigen positive.

Local recurrence rate is lower than some low grade tumour. Metastasis to local lymphnode may be present in 10-20% of cases. Multiple cutaneous deposits and microscopic epidermotropic deposits may develop.

Image link:(Dr.Weems)