Reappraisal of the Confusing Concept “Trichogerminoma” and the Ill-Defined Finding “Cell Balls”: Clinicopathologic Analysis of 6 Cases of Trichogerminoma and Comparison With 2 Cases of Basal Cell Carcinoma With Cell Ball–Like Features

Goto, Keisuke; Takai, Toshihiro; Anan, Takashi; Kimura, Tetsunori; Fukumoto, Takaya; Murai, Hironobu; Nishitani, Nao; Sato, Toshiaki

doi:10.1097/dad.0000000000000921

Cited by 2 publications

(7 citation statements)

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“…To the best of our knowledge, up to now, only 30 trichogerminoma cases have been reported in the literature [15][16][17][18][19][20][21][22][23], a finding which might be explained by the rarity of this entity but also by the lack of established diagnostic criteria [19]. Trichogerminoma is not yet included in the fourth edition of the WHO Classification of Skin Tumours [13] and is regarded by most of the authors as a variant of trichoblastoma [19,47]. In this context, the identification of recurrent genetic alterations, i.e.…”

Section: Discussionmentioning

confidence: 99%

“…Marked Merkel cell hyperplasia turned out to constitute a hallmark feature of the trichogerminoma cases in our series [median Merkel cell density: 364 (range 91–725) Merkel cells/mm 2 ], distinguishing it from other follicular tumours ( p < 0.001) (supplementary material, Figure S5). Accordingly, although not mentioned in the initial report, the presence of Merkel cells has been latterly noticed by some authors in trichogerminomas [16,19], as well as in trichoblastomas [48], and is viewed as a marker of hair follicle differentiation [49]. Indeed, due to their post‐mitotic status [50], Merkel cells in this setting were expected to be due to the abilities of tumour cells to differentiate into Merkel cells [51,52], rather than a colonization of epithelial structures by physiological Merkel cells [53].…”

Section: Discussionmentioning

confidence: 99%

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Recurrent FOXK1::GRHL and GPS2::GRHL fusions in trichogerminoma

Kervarrec

Pissaloux

Poilane

et al. 2022

The Journal of Pathology

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We report 21 cases of trichogerminoma harbouring previously undescribed FOXK1::GRHL1/2 or GPS2::GRHL1/2/3 in‐frame fusion transcripts. Microscopic examination of a preliminary set of five cases revealed well‐delimitated tumours located in the dermis with frequent extension to the subcutaneous tissue. Tumours presented a massive and nodular architecture and consisted of a proliferation of basaloid cells. A biphasic pattern sometime resulting in tumour cell nests (‘cell balls’) was present. Immunohistochemistry demonstrated the expression of cytokeratins (CKs) 15, 17, and PHLDA1. In addition, numerous CK20‐positive Merkel cells were detected. RNA sequencing (RNA‐seq) revealed a FOXK1::GRHL1 chimeric transcript in three cases and a FOXK1::GRHL2 fusion in two cases. In a second series for validation (n = 88), FOXK1::GRHL1/2 fusion transcripts were detected by RT‐qPCR or FISH in an additional 12 trichogerminomas and not in any other follicular tumour entities or basal cell carcinoma cases (n = 66). Additional RNA‐seq analysis in trichogerminoma cases without detected FOXK1::GRHL1/2 rearrangements revealed GPS2::GRHL1 fusion transcripts in two cases, GPS2::GRHL2 in one case, and GPS2::GRHL3 fusion transcript in one case. Therefore, our study strongly suggests that GRHL1/2/3 gene rearrangements might represent the oncogenic driver in trichogerminoma, a subset of follicular tumours characterized by immature features and numerous Merkel cells. © 2022 The Pathological Society of Great Britain and Ireland.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Recurrent FOXK1::GRHL and GPS2::GRHL fusions in trichogerminoma

Kervarrec

Pissaloux

Poilane

et al. 2022

The Journal of Pathology

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“…The stroma shows a moderate number of fibroblasts and mast cells. Occasionally, trichogerminoma showes a connection to the overlying epidermis 11 , containes melanin pigments 5 , 11 , showes focal sebaceous differentiation 11 or pilomatrical differentiation 12 .…”

Section: Discussionmentioning

confidence: 99%

“…Immunoreactivity for CD117 (c-KIT), which is usually negative for follicular tumors 16 , is observed in the tumor nests of “extra-ball areas”. The tumor cells are diffusely positive for β-catenin showing a membranous pattern 11 . Kazakov et al 2 noted in their study that tumor nodules expressed AE1/AE3, CK5/8, CK5/6, Cam5.2, while they were negative for CK20, CK7, and calretinin.…”

Section: Discussionmentioning

confidence: 99%

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A case of trichogerminoma: a rare cutaneous follicular neoplasm

et al. 2021

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Summary 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.

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Reappraisal of the Confusing Concept “Trichogerminoma” and the Ill-Defined Finding “Cell Balls”: Clinicopathologic Analysis of 6 Cases of Trichogerminoma and Comparison With 2 Cases of Basal Cell Carcinoma With Cell Ball–Like Features

Cited by 2 publications

References 11 publications

Recurrent FOXK1::GRHL and GPS2::GRHL fusions in trichogerminoma

Recurrent FOXK1::GRHL and GPS2::GRHL fusions in trichogerminoma

A case of trichogerminoma: a rare cutaneous follicular neoplasm

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