Immature trichoepithelioma: report of six cases

Inguinal keratotic Basal cell carcinoma mimicking giant solitary trichoepithelioma

Keratotic basal cell carcinoma may not only clinically but also histologically share more or less the same features with giant solitary trichoepithelioma. It can be difficult to distinguish these two entities from each other, even for an experienced dermatopathologist. We present an unusual case of inguinal keratotic basal cell carcinoma mimicking giant solitary trichoepithelioma in a 56-year-old woman with a finger-like tumor of 20 years duration. The patient presented with an asymptomatic, skin colored, firm, nonulcerative, nodular lesion. Scanty mitotic activity and apoptotic cells were the histopathologic findings against basal cell carcinoma, whereas absence of papillary mesenchymal bodies, presence of peritumoral lacunae detected only around the solid areas, and accumulation of amyloid-like hyalinized material were the findings in favor of basal cell carcinoma. This case illustrates that keratotic basal cell carcinoma must be taken into account in the differential diagnosis of inguinally located solitary, polypoid masses, especially giant solitary trichoepithelioma.

Trichoepithelioma with "monster" stromal cells

Trichoepithelioma is a benign tumor of trichogenic origin which appears predominantly in childhood or in young adults. Different forms have been described according to clinical and histological features. The authors report a unique variant of trichoepithelioma arising on the limb of a 27-year-old man. The tumor was characterized by the mixture of an atypical fibroxanthomatous proliferation and basaloid epithelial strands of trichoepithelioma. Such histological features have not been previously reported. It raises the question of an additional variant of hair follicle tumor with a mixed epithelial and mesenchymal proliferation.

Cytokeratin expression in trichoblastic fibroma (small nodular type trichoblastoma), trichoepithelioma and basal cell carcinoma

Classical trichoblastic fibroma or small nodular type trichoblastoma (Ackerman) is a rare tumour. This tumour, trichoepithelioma and basal cell carcinoma (BCC) have some overlapping histopathological features. There are only a few reports on immunohistochemical studies in large series of these three neoplasms. We investigated immunostaining patterns of 10 different anticytokeratin (CK) antibodies and several other markers in these neoplasms, comparing them with the patterns in normal adult and fetal skin. In trichoblastic fibroma (three cases), CK1/5/10/14, CK7, CK8/18, CK10/11, CK14, CK17 and CK19 were expressed in the basaloid nests, and CK6 and involucrin were detected in the inner layers of keratinous cysts. Trichoepithelioma (seven cases) expressed CK1/5/10/14, CK8/18, CK14, CK17 and CK19 in the basaloid nests, and CK6, CK10, CK10/11 and involucrin were positive in the keratinous cysts. However, no CK7 expression was observed. Solid and keratotic types of BCC (29 cases) expressed CK1/5/10/14, CK7, CK8/18, CK14, CK17 and CK19 in the basaloid nests. The keratinous cysts in BCC were stained with anti-CK6, CK10, CK10/11 and involucrin antibodies. Coupled with the expression of CK8/18, CK17 and CK19 in the outer root sheath of the adult hair follicle, these three neoplasms shared a keratin phenotype characteristic of the outer root sheath. Judging from our immunohistochemical results, trichoblastic fibroma and BCC cannot be differentiated by their patterns of CK expression. The expression of CK7, which is noted in fetal hair follicles, trichoblastic fibroma and BCC, suggests the presence of subpopulations that retain fetal phenotypic characteristics in these two neoplasms. Although the current concept regards trichoepithelioma and trichoblastic fibroma as a single tumour group, the lack of CK7 expression in trichoepithelioma supports the notion that the two are different.

Trichoblastoma and basal cell carcinoma are neoplasms with follicular differentiation sharing the same profile of cytokeratin intermediate filaments

Trichoblastoma and nodular basal cell carcinoma are generally held to be distinctive epithelial neoplasms with some overlapping features. We investigated 30 trichoblastomas in which the basaloid cells expressed cytokeratins (CK) CK5/6, CK14, CK17, CK19, and, in a few cells, vimentin. The cells of the periphery of small and large cysts showed the same profile. Cells lining the lumen of small cysts expressed CK14, CK17, and involucrin, and those in larger cysts showed a positivity for CK1, CK4, CK10, CK14, CK17, and involucrin. The remaining tested antibodies (CK7, CK8, CK13, CK18, CK20, alpha-smooth-muscle actin) were negative in all cases. The cells of the stroma expressed vimentin and in 22 cases, the CD34 antigen. Seventeen nodular basal cell carcinomas showed exactly the same staining pattern. Furthermore, there are striking immunohistochemical similarities between the neoplastic basaloid cells of both neoplasms and the cells of the hair germ. Therefore, trichoblastoma and nodular basal cell carcinoma cannot be distinguished by their pattern of cytokeratin expression in paraffin sections. The virtually identical cytokeratin pattern seen in trichoblastoma, basal cell carcinoma, and the developing fetal hair follicle is compelling evidence for common differentiation pathway.

Two cases of basal cell carcinoma arising in seborrheic keratosis

The present study reports two cases of basal cell carcinoma arising in seborrheic keratosis. The first case is a seventy-three-year-old female who presented with a blackish nodule arising from a pigmented lesion on her chest. Histopathological analysis of the nodule and the pigmented lesion revealed a basal cell carcinoma with hair follicular differentiation and an acanthotic seborrheic keratosis, respectively. The second case is a seventy-year-old female with a blackish nodule arising from a pigmented lesion on her back. Histological analysis of the nodule revealed an atypical basaloid cell mass surrounded by a seborrheic keratosis lesion. In addition to the coexisting seborrheic keratosis with the basal cell carcinoma, a basaloid follicular hamartoma that showed multiple hamartomatous hair follicles or small cysts replaced by a branching cord or lace-like network of basaloid cells surrounded by fibrovascular stroma was identified. We concluded that both cases presented a rare combination of a seborrheic keratosis which underwent a malignant change to basal cell carcinoma. It appears that both basal cell carcinomas and seborrheic keratosis may derive from a similar source: pluripotential cells of either the epidermis or hair follicle epithelium.

Trichoblastoma with rippled-pattern

The following is a case study of a 36-year-old Japanese man with a trichoblastoma which exhibited a rippled-pattern on the left temporal region of the scalp. The histological findings of the tumor revealed lobular aggregations composed of immature follicular basaloid cells, lobules of squamous eddy-like foci of incomplete keratinization or small keratinous cysts, and multiple papillary mesenchymal bodies similar to hair germ. Interestingly, a rippled-pattern of basaloid cells and hyalinized matrixes resembling the Verocay bodies of neurilemmoma was also observed. We propose that the rippled-pattern of the basaloid cells and hyalinized matrices is caused by the characteristic stromal induction of trichoblastoma.

Trichogerminoma. Report of 14 cases

We report 14 cases of trichogerminoma, a rare form of cutaneous adnexal neoplasm, derived from hair germ epithelium. The neoplasms occurred in 9 men and 5 women. Their ages ranged from 16 to 73 years (median 53 years). The tumors were slow growing, asymptomatic dermal or subcutaneous nodules, located on the head and neck (6), trunk (4), extremities (2) and hip (1), with no distinguishing clinical features. Histologically, trichogerminomas were characterized by sharply circumscribed, pseudoencapsulated dermal and subcutaneous nodules, ranging in size from 0.4 to 4.0 cm in diameter (mean 1.9 cm). The nodules were subdivided into lobules separated by variable amounts of stroma that demonstrated varying cellularity and mucin content. The lobules were composed of basaloid cells that formed densely packed, round nests or "cell balls" resembling hair bulbs. The basaloid cells demonstrated peripheral palisading, keratinization and differentiation towards various pilosebaceous structures. Retraction spaces, well developed hair follicles and hair shafts were not observed. These distinctive histologic features separated these neoplasms from other tumors of pilar origin and from basal cell carcinoma. The trichogerminomas behaved in a benign fashion with one exception. Complete excision of the lesions is the treatment of choice.

Trichoblastic fibroma

We report a trichoblastic fibroma in the groin of a 60-year-old woman. This unusual tumor showed a predominance of epithelial component, with abundant basophilic, well-circumscribed, epithelial lobules and some keratinous cysts. Several areas suggested stromal induction of differentiation, and in the keratinous cysts there were indications of outer hair sheath differentiation. We review the clinical data from published cases of trichogenic hair germ tumors and discuss the differential diagnosis.