A case of trichogerminoma

A case of trichogerminoma: a rare cutaneous follicular neoplasm

Trichogerminoma, first described by Sau et al. in 1992, is a rare cutaneous adnexal neoplasm of the hair germ cell and usually associated with benign clinical course and favorable outcome. About 30 cases have been reported, all with similar histological features. However, due to a small but potential risk of malignancy, complete excision of the tumor is the treatment of choice. There is still controversy over its inclusion into the spectrum of trichoblastoma.

Herein, we report an additional case occurring in the left buttock of a 47-year-old female, presenting with a subcutaneous solitary nodule composed of lobules of basaloid cells, with peripheral palisading and round cell nests or "cell balls" arranged in the central part. The lobules are separated by a fibrous or myxoid stroma. There are no clefts separating the tumor cells and surrounding stroma, but clefts separating stroma by the surrounding adipose tissue can be seen. Typical mitotic figures are frequently present (4-5 per 10 high-power fields). Immunohistochemistry shows the tumor cells are positive for pan-CK (AE1/AE3), CK5/6, p40, GATA 3, whereas they are negative for CK7, CK20, chromogranin A, synaptofisin, androgen receptor, estrogen receptor, and calretinin. Staining for CK20, synaptofisin, and chromogranin A detect Merkel cells scattered within the lobules. Ki67 highlights a nuclear proliferative rate of about 20%.

Trichogerminoma should be distinguished from other trichogenic tumors made up of basoloid cells or hair follicular differentiation. The mainly differential diagnosis includes trichoblastoma, trichoepitelioma, tricholemmoma, and basal cell carcinoma.

Herein, we report a case of trichogerminoma which, unlike the cases previously reported, showed numerous mitotic figures and a higher Ki67 nuclear proliferative rate.

A Case of Trichogerminoma With Pilomatrical Differentiation and a Unique Immunohistochemical Profile

Trichogerminomas are rare adnexal neoplasms first described by Sau et al in 1992. Including the initial report, 20 cases have been reported, all with similar histological features, namely tumor nodules composed of basaloid cells that form densely packed, round nests or "cell balls" and which demonstrate variable degrees of pilosebaceous differentiation. In this study, the authors report a case of a trichogerminoma with pilomatrical differentiation and a unique immunohistochemical profile. The patient is a 71-year-old man with a well-delineated nodule on the top of the scalp. Histologically, the lesion measured 16 mm in greatest dimension and was composed of nodules of basaloid cells with central, compact, slightly eosinophilic cells nests. Immunohistochemically, the tumor nodules diffusely expressed cytokeratins 34βE12, AE1/3, and CK5/6. Diffuse expression of β-catenin and nuclear expression of p63 were also evident. The peripheral basaloid cells, but not the cell balls, expressed CD10, Ber-EP4, BCL-2, and CK7, the latter a previously unreported finding. The histological findings and immunohistochemical profile are compatible with a diagnosis of a trichogerminoma.

Trichogerminoma, a rare cutaneous follicular neoplasm with indolent clinical course: report of two cases and review of literature

Trichogerminoma is a rare cutaneous adnexal neoplasm of the hair germ cell and usually associated with benign clinical course and favorable outcome. Since its first description by Sau et al. in 1992, only a few cases have been reported up to date. Herein, we report two additional cases occurring in the hip and right thigh, respectively. Both patients are male, one is 78 years old, the other is 29 years old. Histological examination reveals well-circumscribed dermal nodule composed of lobules of basaloid cells with surrounding pseudocapsule. The distinct characteristic of the tumor is that most of the lobules display a special pattern of round nests or cell balls arranged in the central part with the peripheral palisading. Immunostaining showed ring-like fashion of CK5/6, P63 and Bcl-2 with negative or weak staining in the "cell balls". There was no recurrence after complete excision during the period of follow-up. To the best of our knowledge, this is the first report of trichogerminoma in Chinese population. In contrast to the previously reported cases, ours present the similar morphological features with distinct immunohistochemical characteristics. We consider the concept of trichogerminoma exists with no doubt by its identifiable morphological features, and it should be classified as a variant of trichoblastoma. Because of its malignant potential, complete excision is a prior choice of treatment for this rare but distinctive tumor.

VIRTUAL SLIDES

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