Fibro-osseous pseudotumor of the digit: a comparison to myositis ossificans by light microscopy and immunohistochemical methods.

Fibro-osseous pseudotumor of the digit is an unusual cutaneous process characterized histologically by a fibroblastic proliferation admixed with reactive/metaplastic osteoid formation. The osteoid formation can be florid and immature, mimicking the appearance of malignant osteoid-forming neoplasms. Fibro-osseous pseudotumor of the digit has histologic and clinical features in common with myositis ossificans. This has led many to consider the two to be synonymous. We studied three cases of fibro-osseous pseudotumor, compared to five cases of myositis ossificans, using routine light microscopy and a battery of immunohistochemical stains. Both entities displayed a "zoning" pattern of immature spindled areas admixed with more mature areas having osteoid metaplasia. This was more pronounced in myositis ossificans. In each lesion, the spindle cells stained positively for vimentin and actin. CD34 and Factor VIII highlighted the vasculature. No stromal staining for MAK-6 (cytokeratin) or S-100 was identified. Ki-67, a proliferation marker, showed positive staining of the stromal cells in both lesions, which was strongest in the immature spindled areas. The immunohistochemical and histologic similarities of the lesions support fibro-osseous pseudotumor of the digit being a cutaneous variant of myositis ossificans.

Subcutaneous Castleman's disease of the wrist.

Castleman's disease usually occurs as a solitary lesion in the mediastinum and less frequently in the neck region. Two variants are recognized, the more common hyaline-vascular type and the plasma cell type. A third hybrid, or intermediate, variant exists that shares features with both the hyaline-vascular and plasma cell types. Uncommonly, these lesions occur outside the mediastinum or neck region. We report a case of subcutaneous Castleman's disease of the intermediate type on the wrist of a 56-year-old woman without systemic symptoms.

Keratoacanthoma: a deficient squamous cell carcinoma? Study of bcl-2 expression.

Ten keratoacanthomas with both proliferative and regressive histologic features along with 10 well-differentiated squamous cell carcinomas were examined using immunohistochemistry for the expression of bcl-2, a protooncogene recently recognized to be involved in protecting cells from undergoing apoptosis. The squamous cell carcinomas had a modest but diffuse staining pattern, while the proliferative keratoacanthomas stained only at the basal cells and only rare cells stained positively in the regressive keratoacanthomas. The degree and pattern of staining suggest a loss of bcl-2 expression with tumor maturity in keratoacanthoma and a possible role in their ultimate involution.

Extramammary Paget's disease associated with prostate adenocarcinoma.

A case of scrotal and penile extramammary Paget's disease (EMPD) and concurrent prostate adenocarcinoma in a 59-year-old patient is presented. Immunohistochemically, the tumor cells of both the EMPD and prostate stained positively for prostate-specific antigen. Six previously reported cases of EMPD associated with prostate adenocarcinoma are reviewed, along with a discussion of current theories of the pathogenesis of EMPD.

Intravascular (angiotropic) large cell lymphoma: determination of monoclonality by polymerase chain reaction on paraffin-embedded tissues.

Angiotropic lymphoma is a rare, aggressive, intravascular non-Hodgkin's lymphoma, usually of B-cell phenotype. Because lymphoma is often clinically unsuspected, the small skin or muscle biopsies typically obtained for evaluation make assessment of lymphoid clonality through cell surface markers or Southern blot hybridization analysis difficult or impossible. The recent development of polymerase chain reaction methodologies to detect chromosomal translocations and immunoglobulin heavy chain gene rearrangement on paraffin-embedded tissue offers an attractive alternative for ascertaining the clonality of lymphoproliferative processes. We report a case of B-cell angiotropic lymphoma in which a monoclonal variable diversity joining region rearrangement of the immunoglobulin heavy chain locus was detected by polymerase chain reaction in both ante- and postmortem, formalin-fixed, paraffin-embedded skeletal muscle. The use of polymerase chain reaction in assessing clonality in angiotropic lymphoma is enhanced by the general absence of a background of reactive B-lymphoid cells in angiotropic lymphoma, which can obscure the monoclonal band and/or compromise sensitivity. No amplification product was obtained for t(14;18) involving the bcl-2 major breakpoint region. It is interesting to note that this case exhibited rare circulating lymphoma cells and more extensive bone marrow involvement (more than 100 tumor cells/high magnification field) than has been previously described.

Proliferating trichilemmal cyst. Report of four cases, two with nondiploid DNA content and increased proliferation index.

Proliferating trichilemmal cyst (PTC) is an uncommon tumor that usually arises on the scalp of elderly women. Its biologic nature is that of a benign lesion with occasional local recurrences. PTC can be confused both grossly and microscopically with squamous cell carcinoma and malignant PTC. Distinction between these lesions has historically been made on a histologic basis. We present four cases of PTC. Histologically, the lesions consisted of lobules of basaloid cells admixed with larger pale-staining cells with abrupt trichilemmal type of keratinization and peripheral palisading embedded in a fibrous stroma. Flow cytometry performed on nuclear extracts of the lesions revealed two of the four lesions to have nondiploid DNA content. Proliferation index, measured by immunohistochemical staining with Ki-67 monoclonal antibody along with mitotic rate count, was higher in the two nondiploid lesions as compared with their diploid counterparts. The results raise the question of the significance of aneuploidy and increased proliferation indices in otherwise benign PTC.