Benign trichogenic tumours: a report of two cases supporting a simplified nomenclature

Unusual Presentation of Trichoblastoma

We report a 39-year-old man who presented with skin-colored plaque over the glabella and root of the nose. Histopathology revealed the diagnosis of trichoblastoma. This case is reported to emphasize the rare presentation of trichoblastoma as it usually presents as an isolated nodule.

Folliculosebaceous neoplasms: A review of clinical and histological features

Numerous benign and occasionally malignant tumors arise from the folliculosebaceous apparatus. Confusing terminology, rarity of malignant variants and overlapping histological features can lead to diagnostic uncertainty. This review highlights the clinical and histopathological features that help to classify these entities, as well as the various syndromes associated with certain members of this large family of tumors.

Trichoblastic sarcoma: a high-grade stromal tumor arising in trichoblastoma

We report a case of primary sarcoma of the skin with a biphasic histological pattern, being composed of areas of mixed mesenchymal-epithelial cell proliferation and areas of purely sarcomatous growth. The tumor occurred in the posterior cervical region of a 93-year-old man, and its history was marked by sudden, rapid enlargement after many years of stable duration. The excised lesion was about 4 cm in diameter, had a firm consistency and was covered by intact skin. Histological examination showed a multifocal proliferation of follicular germinative cells arranged in corymbiform and petaloid shapes with an overall retiform growth pattern. Epithelial cords and strands were composed of cytologically uniform cells with bland nuclear features and were surrounded by a prominent, fibroblast-rich stroma reminiscent of a perifollicular sheath. In many areas of the tumor the stroma showed abrupt transition into a pleomorphic proliferation of large sarcomatous cells with frequent and often atypical mitoses. Multinucleated neoplastic cells infiltrated the epithelial structures to cause their partial or total obliteration in many fields of the lesion. Immunohistochemically, the epithelial cells displayed expression of various keratins, with a particularly intense staining for 34betaE12, and were partly positive for the CD10 antigen. A strong immunostaining for this antigen was also observed in malignant-appearing stromal areas, where no expression of cytokeratins was detected. Moreover, nuclear positivity for p53 protein was seen in sarcomatous cells, whereas it resulted in total lack of epithelial elements. Our case emphasizes that high-grade sarcoma may occur in the spectrum of trichoblastic tumors and that it may share some features of other noncutaneous biphasic neoplasms, such as mammary cystosarcoma phyllodes.

An unusually aggressive trichoblastoma

Trichogenic tumors are neoplasms of the hair germ cell that usually exhibit benign behavior. We describe a case of a large invasive trichoblastoma requiring Mohs micrographic surgery for its removal. Immunohistochemical studies performed demonstrate overlapping features of this trichogenic tumor with basal cell carcinoma.

Subcutaneous trichoblastoma

We have recently observed three examples of solitary trichoblastomas (TB) with unusual histopathologic features characterized mainly by numerous aggregations of basaloid cells limited to the subcutis. The three trichoblastomas with unusual features were identified from a large series of 38 solitary TB cases collected over a period of 20 years. Clinically, all three neoplasms presented in men (49, 52, and 62 years old) as solitary, 1- to 1.5-cm skin-colored nodules situated on the scalp, face, and lower arm, respectively. Histopathologically, they showed numerous, smooth-bordered aggregations of basaloid cells limited to the subcutis and surrounded by a sclerotic and partly hyalinized stroma. Multiple sections revealed no connections of basaloid aggregations to the overlying epidermis or pre-existing follicular structures. All three cases displayed rather unusual morphologic growth patterns, including areas of variously sized, nodular aggregations of basaloid cells and extensive foci of elongated, thin columns and branching cords of basaloid cells. A striking feature in the stromal component in two cases was the presence of large, prominent areas of hyalinization and sclerosis. Characteristically, all three neoplasms showed numerous foci with rudimentary follicular germs and papillae. Cytomorphologically, the basaloid cells exhibited dark staining nuclei with large prominent nucleoli and scanty, pale or eosinophilic cytoplasm. Variable number of mitotic figures (2-4 mitoses per high-power field) and single necrotic cells were noted. In one case, small, foci of necrosis en masse were observed. Follow-up data after total excision in all three cases (80, 69, and 6 months) revealed no local recurrences. In light of our observations, we suggest that subcutaneous TB represents a rare variant of solitary TB. Besides the exclusive subcutaneous location, this neoplasm also displays a constellation of particular histopathologic features, namely, rather complex epithelial growth patterns and stroma with prominent foci of sclerosis and hyalinization.

Benign cutaneous adnexal tumors with combined folliculosebaceous, apocrine, and eccrine differentiation. Clinicopathologic and immunohistochemical study of eight cases

Benign cutaneous adnexal tumors displaying divergent differentiation are rare, with very few well-documented cases reported in the literature. We describe eight cases of benign adnexal tumors showing a variable combination of eccrine, apocrine, and folliculosebaceous differentiation. Clinically, all tumors presented as solitary, slowly enlarging dermal or subcutaneous nodules located in the head and neck and the extremities. Histologically, they were characterized by well-circumscribed, unencapsulated nodules composed of a lobular proliferation of epithelial cells displaying a spectrum of trichogenic, sebaceous, apocrine, and eccrine differentiation. The histological spectrum included lobules and trabeculae of basaloid cells with glandular and ductal elements, well-formed folliculosebaceous units, primitive follicles, and foci of tricholemmal keratinization. Immunohistochemical evaluation in four cases showed similar cytokeratin, carcinoembryonic antigen, and epithelial membrane antigen staining profiles as those reported for sweat gland adenomas; in addition, focal S-100 protein positivity and GCDFP-15 positivity could also be demonstrated, suggesting eccrine-apocrine differentiation. The tumors were most frequently confused histologically with other adnexal neoplasms, including sebaceoma, sebaceous adenoma, basal cell carcinoma, chondroid syringoma, and trichoepithelioma. The present series highlights the capability.