Microcystic adnexal carcinoma is an unusual locally aggressive neoplasm that is important to recognize since it may be confused with benign adnexal neoplasms, particularly desmoplastic trichoepithelioma, trichoadenoma, and syringoma. Six cases are described all of which displayed benign histological features on initial biopsy. Most often these neoplasms presented as solitary flesh‐colored indurated plaques on the upper lip. All patients were white, five were women, and the average age was 44‐years‐old. Islands of basaloid keratinocytes, some of which contained horn cysts and abortive follicles, were embedded in a desmoplastic stroma. In other foci, ducts and gland‐like structures lined by a two‐cell layer predominated. In deep components individual and thin strands of cells dissected collagen bundles and skeletal muscle and invaded perineural spaces. Despite this, cytologic atypia and mitotic figures were rare. The cell of origin is considered to be a pluripotential adnexal keratinocyte which is capable of both follicular and sweat gland differentiation.

Cutaneous squamous cell carcinoma (SCC) includes many subtypes with widely varying clinical behaviors, ranging from indolent to aggressive tumors with significant metastatic potential. However, the tendency for pathologists and clinicians alike is to refer to all squamoid neoplasms as generic SCC. No definitive, comprehensive clinicopathological system dividing cutaneous SCCs into categories based upon their aggressiveness has yet been promulgated. Therefore, we have proposed the following based upon the malignant potential of SCC variants, separating them into categories of low (< or = 2% metastatic rate), intermediate (3-10%), high (greater than 10%), and indeterminate behavior. Low-risk SCCs include SCC arising in actinic keratosis, HPV-associated SCC, tricholemmal carcinoma, and spindle cell SCC (unassociated with radiation). Intermediate-risk SCCs include adenoid (acantholytic) SCC, intraepidermal epithelioma with invasion, and lymphoepithelioma-like carcinoma of the skin. High-risk subtypes include de novo SCC, SCC arising in association with predisposing factors (radiation, burn scars, and immunosuppression), invasive Bowen's disease, adenosquamous carcinoma, and malignant proliferating pilar tumors. The indeterminate category includes signet ring cell SCC, follicular SCC, papillary SCC, SCC arising in adnexal cysts, squamoid eccrine ductal carcinoma, and clear-cell SCC. Subclassification of SCC into these risk-based categories, along with enumeration of other factors including tumor size, differentiation, depth of invasion, and perineural invasion will provide prognostically relevant information and facilitate the most optimal treatment for patients.

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