Follicular squamous cell carcinoma of the skin: a poorly recognized neoplasm arising from the wall of hair follicles.

Background: In the last decades, a number of clinicopathologic subtypes of squamous cell carcinoma (SCC) of the skin, ranging from highly aggressive tumors with a tendency to recur and metastasize to neoplasms with a favorable prognosis, have been described. SCCs arising from the wall of hair follicles have been briefly mentioned by some authors but never reported in a series.

Methods: Cases of SCC arising from the wall of hair follicles were collected from the files of two large German Centers for Dermatopathology and analyzed clinicopathologically and immunohistochemically.

Fibroblastic/myofibroblastic sarcoma of the skin: a report of five cases.

Background: A number of malignant soft tissue tumors, particularly those of fibroblastic and fibrohistiocytic derivation, have been found to display myofibroblastic differentiation focally. The term myofibroblastic sarcoma, a controversial presumably distinctive entity, defines a malignant soft tissue tumor in which myofibroblasts are quantitatively the predominant cell type.

Methods: Five cases of cutaneous spindle-cell sarcomas showing fibroblastic-myofibroblastic differentiation with predominance of fibroblasts were retrieved from the files of three large centers of dermatopathology.

Pigmented atypical fibroxanthoma: a tumor that may be easily mistaken for malignant melanoma.

Nine cases of an unusual presentation of atypical fibroxanthoma that we previously termed pigmented atypical fibroxanthoma are reported. Pigmented atypical fibroxanthoma can be easily mistaken for malignant melanoma both clinically and histopathologically. The resemblance of pigmented atypical fibroxanthoma to melanoma is secondary to the ability of neoplastic cells to ingest and degrade erythrocytes following intratumoral hemorrhage and to accumulate hemosiderin in their cytoplasm.

Malignant fibrous histiocytoma of the skin with marked inflammatory infiltrate: a sarcoma mimicking malignant lymphoma.

Three cases of malignant fibrous histiocytoma of the skin with a marked inflammatory infiltrate in the stroma are reported. The inflammatory infiltrate, composed mainly of T-lymphocytes, obscured the nature of the neoplasms, and immunohistochemical studies were required to establish the diagnosis. Two tumors arose in the sun-damaged skin of the face, and one tumor arose in the chest wall.

Subcutaneous pseudomembranous fat necrosis: new observations.

Background: Pseudomembranous fat necrosis is a peculiar manifestation of necrosis of adipose tissue characterized by formation of pseudocystic cavities lined by crenulated membranes. The underlying mechanism for the formation of pseudomembranes is unknown and numerous hypotheses have been proposed. Despite divergent interpretations, most authors consider necrotic fat cells to be the anatomic substrate for the formation of pseudomembranes.