Trichogerminoma: A Rare Cutaneous Adnexal Tumor with Differentiation toward the Hair Germ Epithelium

Abstract

In 1992, Sau and colleagues described 14 cases of a rare cutaneous adnexal tumor with differentiation toward the hair germ epithelium. All cases in their study displayed a unique constellation of histological features which allowed the authors to consider the neoplasm to be a distinct entity and to designate it as ‘trichogerminoma’ (TG). We present a case of an adnexal tumor identical to that described as TG and report the immunophenotypical features of this neoplasm for the first time. A biopsy from a 41-year-old man revealed a well-demarcated epithelial tumor composed of multiple lobules located in the deep dermis without connection to the overlying epidermis and surrounded by a fibrous pseudocapsule. The tumorous lobules were composed of uniform basophilic cells with vesicular nuclei, dispersed chromatin and prominent nucleoli showing no prominent peripheral palisading. Some of the lobules had the appearance of densely packed ‘cell balls’ with peripheral condensation of the tumor cells. The stroma showed a moderate number of fibroblasts and mast cells. Reticulum staining revealed fine reticulum fibers surrounding the tumor aggregates with accentuation of the ‘cell balls’. Immunohistochemically, the tumor cells expressed AE1/AE3, CK5/8, CK5/6, CAM5.2 and stained negatively for CK20, CK7, calretinin, Lu-5 and Thomsen- Friedensreich antigen. There was no increase in the numbers of CK20-positive Merkel cells in the epidermis overlying the tumor; however, a few Merkel cells were scattered in some tumor lobules. In addition, we stained 6 trichoblastomas (TBs) and found a particular pattern of calretinin expression in this tumor which was not observed in our case of TG. We conclude that pathological features allow the delineation of TG as a distinct adnexal neoplasm. Histological differential diagnosis includes basal-cell carcinoma (pilar type), large nodular TB, trichoblastic fibroma, trichoepithelioma, tricholemmoma, pilomatricoma and matrical carcinoma.

Trichogerminoma

“…The immunohistochemical analysis performed also confirmed the sebaceous nature of the foci of clear vacuolated cells and duct differentiation and the presence of scattered dendritic S100 protein cells within the tumor, a finding not unexpected in neoplasms of the hair germ. 7 In contrast with the study of Kazakov et al, 3 we did not find immunohistologic evidence of Merkel cells within the neoplasm. This could be related to the lower specificity of CAM5.2 we used when compared with CK20, used by Kazakov et al as marker of neuroendocrine differentiation.…”

Immunohistochemical Study of Calretinin in Normal Skin and Cutaneous Adnexal Proliferations

“…These findings are consistent with those of the cytokeratin expression because cytokeratin pattern in pilomatricoma is similar to that of the outer root sheath of the normal hair follicle. [32][33][34] Proliferating tricholemmal tumors included in this study proved to be positive for calretinin in the neoplastic cell layers close to the lumen of the cystic structures (Fig. 7), supporting their differentiation toward the innermost cell layer of the outer root sheath of the normal hair follicle in anagen.…”

A Case of Trichogerminoma

“…Most Immunohistochemically, the tumor cells express a ringlike staining pattern of cytokeratin markers such as AE1/ AE3, CK5/8 and CK5/6 with prominent immunoreactivity in the peripheral rims of the lobules 2,3 . These results may reflect outer root sheath differentiation 5 .…”

“…Trichogerminoma has a benign course. All the cases, except for one case of undifferentiated carcinoma that developed from trichogerminoma and that ended in death due to metastasis and progression of the disease, have shown no recurrence after surgical removal [1][2][3][4] . Because of the potential of malignancy, complete excision of the tumor should be the treatment of choice.…”

“…Trichogerminoma is an uncommon tumor that originates from hair germ cells and it was first reported on by Sau et al 1 in 1992. Kazakov et al 2 showed the immunohistochemical uniqueness of trichogerminoma and the tumor was confirmed as being a unique entity, yet there is still controversy about this. Therefore, additional observation and research are needed to clarify its features.…”