Microcystic adnexal carcinoma, MAC

Locally aggressive adnexal carcinomas of the skin were subdivided by Puijol into:

type 1 - pilar differentiation
- type 1a - purely pilar
- type 1b - pilar + sudoriparous = microcystic adnexal carcinoma
- type 1c - sebaceous-pilar +/- sudoriparous
type 2 - purely sudoriparous = sweat gland carcinomas

Clinical features

MACs occur mainly on the head and neck, on chronically sun-exposed skin.

Histopathology

MACs show nodules, strands , cords and nests of deceptively bland epithelial cells. there is frequently a sclerotic stroma. There are varying degrees of microcyst formation.

Immunohistochemistry

	MAC	Sclerosing type basal cell carcinoma	Desmoplastic trichoepithelioma
AE1/3	10/10	10/10	4/4
CK7	10/10	0/10	0/4
CK20	0/10	0/10	0/4
bcl-2	10/10	10/10	0/4
EMA	10/10	0/10	0/4
Ber-EP4	10/10	10/10	4/4
SMA	10/10	4/10	0/4
S-100	10/10	0/10	0/4
CD34	0/10	0/10	0/4
c-erbB-2	0/10	0/10	0/4
Ki-67	all cases, <5% of cells	20% to 40% of cells	rare positive cells
p53	sparse nuclear staining	8/10 intense	rare positive cells

Differential diagnosis

Other skin tumours including sclerosing type basal cell carcinoma and desmoplastic trichoepithelioma.

References

KJ Smith et al. Microcystic adnexal carcinoma: an immunohistochemical study including markers of proliferation and apoptosis. Am J Surg Pathol 2001;25:464-471.

This page last revised 30.4.2001.