Recurrent PAK2 rearrangements in poroma with folliculo-sebaceous differentiation.

AIMS: Poroma is a benign adnexal neoplasm with differentiation towards the upper portion of the sweat gland apparatus. In 2019, Sekine et al. demonstrated recurrent YAP1::MAML2 and YAP1::NUTM1 fusion in poroma and porocarcinoma. Follicular, sebaceous and/or apocrine differentiation has been reported in rare cases of poroma and whether these tumours constitute a variant of poroma or represent a distinctive tumour is a matter to debate. Herein we describe the clinical, immunophenotypic, and molecular features of 13 cases of poroma with folliculo-sebaceous differentiation. METHODS AND RESULTS: Most of the tumours were located on the head and neck region (n = 7), and on the thigh (n = 3). All presented were adults with a slight male predilection. The median tumour size was 10 mm (range: 4-25). Microscopically, lesions displayed features of poroma with nodules of monotonous basophilic cells associated with a second population of larger eosinophilic cells. In all cases, ducts and scattered sebocytes were identified. Infundibular cysts were present in 10 cases. In two cases high mitotic activity was noted, and in three cases cytologic atypia and areas of necrosis were identified. Whole transcriptome RNA sequencing demonstrated in-frame fusion transcripts involving RNF13::PAK2 (n = 4), EPHB3::PAK2 (n = 2), DLG1::PAK2 (n = 2), LRIG1::PAK2 (n = 1), ATP1B3::PAK2 (n = 1), TM9SF4::PAK2 (n = 1), and CTNNA1::PAK2 (n = 1). Moreover, fluorescence in situ hybridisation (FISH) analysis revealed PAK2 rearrangement in an additional case. No YAP1::MAML2 or YAP1::NUTM1 fusion was detected. CONCLUSION: Recurrent fusions involving the PAK2 gene in all analysed poroma with folliculo-sebaceous differentiation in this study confirms that this neoplasm represents a separate tumour entity distinct from YAP1::MAML2 or YAP1::NUTM1 rearranged poromas.

Acquired smooth muscle hamartoma with sebaceous component.

BACKGROUND: Acquired smooth muscle hamartoma (ASMH) is a rare benign lesion characterized clinically by hyperpigmented plaques with hypertrichosis and some follicular papules. The main histologic finding is the presence of disorganized smooth muscle bundles in the dermis. Only 25 cases of ASMH have been reported in the literature. CLINICAL CASE: We present the case of an 18-year-old male who reported a pigmented area and increased hair growth on the left hemifacial with one year of evolution. Clinically, a plaque was observed in the preauricular region and on the left cheek with a linear Blaschkoid path, consisting of hyperpigmentation, hypertrichosis, and some papular lesions, with negative pseudo-Darier sign. Histological analysis showed an increase in the number of smooth muscle bundles in the middle and deep dermis surrounding abundant sebaceous glands and numerous hair follicles in different stages of evolution. CONCLUSIONS: The sebaceous component in this lesion was prominent. Therefore, we considered this lesion part of a spectrum where the acquired smooth muscle hamartoma and folliculosebaceous cystic hamartoma are found at the extremes. This case would fall in the middle of the range, as it combines both histological features.

INTRODUCCIÓN: El hamartoma de músculo liso adquirido (HMLA) es una lesión benigna adquirida, poco frecuente, caracterizada clínicamente por presentar placas hiperpigmentadas, con hipertricosis y algunas pápulas foliculares. El principal hallazgo histológico es la presencia de abundantes haces de músculo liso desorganizados en la dermis. Se han reportado solo 25 casos de HMLA en la literatura. CASO CLÍNICO: Se presenta el caso de un paciente de sexo masculino de 18 años que refirió una zona pigmentada y el aumento de vello en la hemicara izquierda con un año de evolución. Clínicamente se observó una placa en la región preauricular y mejilla izquierda con trayecto lineal blaschkoide, constituida por hiperpigmentación, hipertricosis y algunas lesiones papulares, con signo pseudo-Darier negativo. Histológicamente se encontró un aumento en el número de haces de músculo liso en la dermis media y profunda rodeando abundantes glándulas sebáceas, así como numerosos folículos pilosos en diferentes estadios de evolución. CONCLUSIONES: El componente sebáceo en esta lesión fue muy marcado, por lo que se considera que forma parte de un espectro donde en los extremos se encuentran el hamartoma de músculo liso adquirido y el hamartoma quístico folículo sebáceo. El presente caso se encontraría en medio, ya que combina ambas características histológicas.

Acquired smooth muscle hamartoma with sebaceous component / Hamartoma de músculo liso adquirido con componente sebáceo

Abstract Background: Acquired smooth muscle hamartoma (ASMH) is a rare benign lesion characterized clinically by hyperpigmented plaques with hypertrichosis and some follicular papules. The main histologic finding is the presence of disorganized smooth muscle bundles in the dermis. Only 25 cases of ASMH have been reported in the literature. Clinical case: We present the case of an 18-year-old male who reported a pigmented area and increased hair growth on the left hemifacial with one year of evolution. Clinically, a plaque was observed in the preauricular region and on the left cheek with a linear Blaschkoid path, consisting of hyperpigmentation, hypertrichosis, and some papular lesions, with negative pseudo-Darier sign. Histological analysis showed an increase in the number of smooth muscle bundles in the middle and deep dermis surrounding abundant sebaceous glands and numerous hair follicles in different stages of evolution. Conclusions: The sebaceous component in this lesion was prominent. Therefore, we considered this lesion part of a spectrum where the acquired smooth muscle hamartoma and folliculosebaceous cystic hamartoma are found at the extremes. This case would fall in the middle of the range, as it combines both histological features.

Resumen Introducción: El hamartoma de músculo liso adquirido (HMLA) es una lesión benigna adquirida, poco frecuente, caracterizada clínicamente por presentar placas hiperpigmentadas, con hipertricosis y algunas pápulas foliculares. El principal hallazgo histológico es la presencia de abundantes haces de músculo liso desorganizados en la dermis. Se han reportado solo 25 casos de HMLA en la literatura. Caso clínico: Se presenta el caso de un paciente de sexo masculino de 18 años que refirió una zona pigmentada y el aumento de vello en la hemicara izquierda con un año de evolución. Clínicamente se observó una placa en la región preauricular y mejilla izquierda con trayecto lineal blaschkoide, constituida por hiperpigmentación, hipertricosis y algunas lesiones papulares, con signo pseudo-Darier negativo. Histológicamente se encontró un aumento en el número de haces de músculo liso en la dermis media y profunda rodeando abundantes glándulas sebáceas, así como numerosos folículos pilosos en diferentes estadios de evolución. Conclusiones: El componente sebáceo en esta lesión fue muy marcado, por lo que se considera que forma parte de un espectro donde en los extremos se encuentran el hamartoma de músculo liso adquirido y el hamartoma quístico folículo sebáceo. El presente caso se encontraría en medio, ya que combina ambas características histológicas.

A Case of Trichoblastoma with Trichoepithelioma-like and Sebaceous Differentiation / 대한피부과학회지

We report a 40-year-old woman with trichoblastoma on vertex scalp showing trichoepithelioma-like feature in upper part and focal sebaceous differentiation. The co-presence of trichoblastoma and trichoepithelioma-like feature in a same tumor represented that the inclusive term trichoblastoma is better for trichogenic tumors composed of follicular germinative cells, and sebaceous differentiation meant the common embryonic origin of folliculo-sebaceous-apocrine unit.