Gene fusions in poroma, porocarcinoma and related adnexal skin tumours: An update.

Poroma is a benign sweat gland tumour showing morphological features recapitulating the superficial portion of the eccrine sweat coil. A subset of poromas may transform into porocarcinoma, its malignant counterpart. Poroma and porocarcinoma are characterised by recurrent gene fusions involving YAP1, a transcriptional co-activator, which is controlled by the Hippo signalling pathway. The fusion genes frequently involve MAML2 and NUTM1, which are also rearranged in other cutaneous and extracutaneous neoplasms. We aimed to review the clinical, morphological and molecular features of this category of adnexal neoplasms with a special focus upon emerging differential diagnoses, and discuss how their systematic molecular characterisation may contribute to a standardisation of diagnosis, more accurate classification and, ultimately, refinement of their prognosis and therapeutic modalities.

Spindle cell porocarcinoma with a novel YAP1::MAML3 fusion.

Porocarcinomas are rare sweat gland cancers representing the malignant counterpart to benign poromas. Their diagnosis can be challenging, especially in the absence of an associated poroma or when the tumor is poorly differentiated. Since recurrent YAP1::MAML2 and YAP1::NUTM1 fusions have been identified in poroid tumors, molecular studies provide an opportunity to support the diagnosis in challenging cases. We describe a case of a female patient in her early 90s, with a polypoid mass of the hip. Histopathologically, there was a poorly differentiated malignant spindle cell tumor adjacent to a poroma. Because of the close association with a poroma and immunoreactivity for p40, a diagnosis of spindle cell porocarcinoma was rendered, which was further supported by YAP1 immunohistochemical studies. Antibodies targeting both the N-terminus and C-terminus confirmed YAP1 rearrangement in both the poroma and the spindle cell neoplasm. Subsequent targeted RNA sequencing revealed a YAP1::MAML3 gene fusion. MAML3 has previously not yet been reported as a YAP1 fusion partner in porocarcinoma. With the illustration of a rare spindle cell variant of porocarcinoma and the identification of a novel gene fusion, this case report expands the spectrum of morphologic and genomic aberrations associated with porocarcinoma.

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.

Distinct regulations driving YAP1 expression loss in poroma, porocarcinoma and RB1-deficient skin carcinoma.

AIMS: Recently, YAP1 fusion genes have been demonstrated in eccrine poroma and porocarcinoma, and the diagnostic use of YAP1 immunohistochemistry has been highlighted in this setting. In other organs, loss of YAP1 expression can reflect YAP1 rearrangement or transcriptional repression, notably through RB1 inactivation. In this context, our objective was to re-evaluate the performance of YAP1 immunohistochemistry for the diagnosis of poroma and porocarcinoma. METHODS AND RESULTS: The expression of the C-terminal part of the YAP1 protein was evaluated by immunohistochemistry in 543 cutaneous epithelial tumours, including 27 poromas, 14 porocarcinomas and 502 other cutaneous tumours. Tumours that showed a lack of expression of YAP1 were further investigated for Rb by immunohistochemistry and for fusion transcripts by real-time PCR (YAP1::MAML2 and YAP1::NUTM1). The absence of YAP1 expression was observed in 24 cases of poroma (89%), 10 porocarcinoma (72%), 162 Merkel cell carcinoma (98%), 14 squamous cell carcinoma (SCC) (15%), one trichoblastoma and one sebaceoma. Fusions of YAP1 were detected in only 16 cases of poroma (n = 66%), 10 porocarcinoma (71%) all lacking YAP1 expression, and in one sebaceoma. The loss of Rb expression was detected in all cases except one of YAP1-deficient SCC (n = 14), such tumours showing significant morphological overlap with porocarcinoma. In-vitro experiments in HaCat cells showed that RB1 knockdown resulted in repression of YAP1 protein expression. CONCLUSION: In addition to gene fusion, we report that transcriptional repression of YAP1 can be observed in skin tumours with RB1 inactivation, including MCC and a subset of SCC.

YAP1::MAML2 fusions in poromatosis: A report of two patients.

Poromatosis is a rare condition characterized by the development of multiple poromas, mainly reported in patients with a history of malignancy. Recently, frequent YAP1::MAML2 and YAP1::NUTM1 fusions have been described in poromas and porocarcinomas. To date, the molecular features of poromatosis have been investigated in one patient only, wherein the poromas harbored YAP1::MAML2 fusions. Herein, we present two additional cases of poromatosis with YAP1::MAML2 fusions. Case 1: An 81-year-old woman presented with nine papules on the scalp, trunk, and extremities persisting for a year. She had a history of breast cancer, with no information on the treatment. Seven papules were excised. Case 2: A 65-year-old woman presented with 21 lesions on her trunk and lower extremities persisting for 2 years. She had been diagnosed with breast cancer 11 years prior and had undergone partial mastectomy, radiotherapy, chemotherapy, and endocrine therapy. Four lesions were excised. All 11 lesions in both patients were histopathologically similar: anastomosing cords and strands extending from the epidermis, and poroid and cuticular cell proliferation with interspersed small ducts. The tumors showed diffuse nuclear expression of YAP1 N-terminus and loss of YAP1 C-terminus expression. No lesions showed NUT immunopositivity. Sanger sequencing identified YAP1::MAML2 fusions in the poromas of both patients.

The role of line-field confocal optical coherence tomography (LC-OCT) in the diagnosis of eccrine poroma: A case report.

Poroma is skin cancer that arises from the sweat gland cells. Its diagnosis could be difficult. Line-field optical coherence tomography (LC-OCT) is a novel imaging technique that has shown promise in the diagnosis and monitoring of various skin conditions. We report a case of poroma diagnosed by LC-OCT.

Combined tumour of aberrant cytokeratin expressing acral lentiginous melanoma and poroma: Diagnostic challenge.

Combined tumours are uncommon and therefore these tumours may pose a diagnostic challenge. In the current case report, it is aimed to present the clinicopathological features of a combined tumour including melanoma with aberrant cytokeratin expression and poroma.

Fusion-positive skin/adnexal carcinomas.

Gene fusions have been increasingly identified as central events driving oncogenesis in a variety of benign and malignant neoplasms of different histogenesis originating in diverse organs. While some fusion-driven neoplasms may occur at any body site, certain genotypes and their associated phenotypic entities cluster to specific body site/organ, albeit with variable frequencies among anatomic locations. In the last two decades, several skin adnexal entities driven by specific fusions have been described; some of them represent new entities (eg, secretory carcinoma harboring NTRK fusions), while others are old established entities with newly discovered underlying gene fusions (eg, poroid neoplasms harboring NUTM1, YAP1, and WWTR1 fusions). While limited availability of next generation sequencing tools in routine practice has largely limited and delayed discovery of fusions in old entities, the increasing availability of novel immunoantibodies as surrogates to recognize gene fusions (such as NUT and YAP1 immunohistochemistry) represents a relatively cheap, quick, and reliable routine tool for their proper recognition and appropriate classification. This review highlights the main, recently defined skin adnexal carcinomas carrying gene fusions.

Poroma: A Retrospective Series of 80 Patients at a Tertiary Care Hospital. / Poroma. Estudio retrospectivo de 80 pacientes en un hospital terciario.

BACKGROUND: Poroma is a benign, exclusively cutaneous, adnexal tumor with a predilection for palmoplantar skin. OBJECTIVE: To analyze the clinical characteristics of poroma in our population. MATERIAL AND METHODS: Retrospective study of patients diagnosed with poroma between 2002 and 2021. We conducted a chart review to record age; sex; number, location, and diameter of lesions; time since onset; clinical characteristics; suspected clinical diagnosis; resection margin status; recurrences; and follow-up duration. Categorical variables were compared using the Fisher exact test. Continuous variables were compared using the t test or the Mann-Whitney U test depending on whether they were normally or nonnormally distributed. RESULTS: We studied 80 patients (31 women and 49 men) with a median (interquartile range [IQR]) age of 65.5 (29) years. Median time since onset of poroma was 12 (21) months. Median lesion diameter was 8(7)mm, and none of the patients had multiple lesions. The lesions were located on the head and neck in 13 cases, the trunk in 13, the upper extremities in 11, and the lower extremities in 43. Twenty-three lesions (28.8%) were located at acral sites (5 on the palms and 18 on the soles). Women were more likely to have scalp lesions (P=.041). Acral lesions were more likely to be erythematous (P=.014). Five patients experienced local recurrence. CONCLUSIONS: Although poromas are particularly common in acral locations (especially the feet), most of the lesions in our series (71.3%) were located elsewhere. Acral lesions were more likely to show the classic clinical features of erythema and exophytic growth.

The role of reflectance confocal microscopy in the diagnosis of eccrine poroma: A retrospective case-control study.

Eccrine poroma (EP) is a rare benign adnexal tumor that may mimic benign or malignant tumors and differential diagnosis may be difficult under clinical and dermoscopic examination. Reflectance confocal microscopy (RCM) examination may add important information to diagnosis and subsequent management of solitary lesions for which dermoscopy can be challenging. The aim of the present study was to investigate features of EP at RCM in order to detect the characteristics that might aid in the differential diagnosis of EP versus other solitary lesions (benign or malignant). Secondary objective was to correlate the resulting features with histopathological findings. This monocentric retrospective observational case-control study included all EPs registered with RCM between January 2007 and May 2018. Control cases were benign or malignant lesions similar in clinical appearance, morphology, and dermoscopic features to EPs. RCM evaluators were blinded to clinical-dermoscopic images and to final histopathological diagnoses. Finally, RCM-histopathological correlation was performed. A total of 11 EPs and 33 controls were included in the present study. Among RCM parameters, "cords without palisading," "dark holes," "prominent vascularization" and "abundant stroma" resulted positively associated with EP in univariate analysis. RCM features correspond to the histopathological diagnosis of EP in 97% of cases, as illustrated by the cluster analysis. An excellent correlation between diagnostic features of conventional histopathology and RCM was observed. RCM assists in the differential diagnosis of solitary lesions, allowing to reach a correct diagnosis of EP through the identification of its four characteristics.

Merkel cell polyomavirus is a passenger virus in both poroma and porocarcinoma.

BACKGROUND: Merkel cell polyomavirus (MCPyV) has been studied in several malignant and nonmalignant tissues. However, only in Merkel cell carcinoma (MCC) has the connection to tumorigenesis been established. Previously, eccrine porocarcinoma samples were shown to express MCPyV in the majority of samples. We aimed to examine MCPyV in porocarcinoma and poroma samples using MCC as the reference material. METHODS: We analyzed 17 porocarcinoma and 50 poroma samples for the presence of MCPyV using LT antigen immunostaining and DNA detection methods. In addition, 180 MCC samples served as controls. RESULTS: MCPyV LT antigen immunostaining was detected in 10% of poroma and 18% of porocarcinoma samples; on the other hand, it was present in 65% of MCC samples. MCPyV DNA was detected in only 10% of poroma and porocarcinoma samples compared with 96% of MCC samples. The viral DNA copy number in all MCPyV DNA-positive MCCs was at least 25 times higher than that in porocarcinoma or poroma samples with the highest MCPyV DNA-to-PTPRG ratio. CONCLUSIONS: The low number of viral DNA copies in poroma and porocarcinoma samples, together with the negative LT expression of MCPyV DNA-positive tumors, indicates that MCPyV is simply a passenger virus rather than an oncogenic driver of porocarcinoma.

Molecular analysis of NUT-positive poromas and porocarcinomas identifies novel break points of YAP1::NUTM1 fusions.

BACKGROUND: Poromas, and their malignant counterparts, porocarcinomas, harbor recurrent translocations involving YAP1-MAML2, YAP1-NUTM1, and infrequently WWTR1-NUTM1; YAP1-NUTM1 being the most common in porocarcinomas. NUT immunohistochemistry (IHC) can be used to identify NUTM1-translocated tumors. This study sought to investigate potential novel NUTM1-fusion partners among NUT IHC-positive poromas and porocarcinomas. METHODS: Thirteen NUT IHC-positive poroid tumors (four poromas and nine porocarcinomas) were identified within a multi-institutional international cohort. Next-generation sequencing (NGS) assessed for NUTM1 fusion partners. RESULTS: NGS detected a NUTM1 fusion in 12 of 13 cases: YAP1-NUTM1 (11/12 cases) and WWTR1-NUTM1 (1/12 cases). Two of the cases (2/12) with NUTM1 fusion were not called by the NGS algorithm but had at least one read-spanning YAP1-NUTM1 break point upon manual review. A NUTM1 fusion was not identified in one case; however, the sample had low RNA quality. The following fusion events were identified: YAP1 exon 4::NUTM1 exon 3 in six cases, YAP1 exon 6::NUTM1 exon 2 in one case, YAP1 exon 3::NUTM1 exon 3 in three cases, WWTR1 exon 3::NUTM1 exon 3 in one case, and YAP1 exon 8::NUTM1 exon 3 fusion in one case. CONCLUSION: While no novel NUTM1 fusion partners were identified within our cohort, 12 of 13 cases had discoverable NUTM1 fusions; YAP1-NUTM1 fusion was detected in 11 cases (92%) and WWTR1-NUTM1 in 1 case (8%). These data corroborate findings from other recent investigations and further substantiate the utility of NUT IHC in diagnosing a subset of poroid neoplasms. In addition, two of our cases harbored fusions of YAP1 exon 6 to NUTM1 exon 3 and YAP1 exon 8 to NUTM1 exon 2, which have not been reported before in poroid neoplasms and indicate novel break points of YAP1.

A case of YAP1 and NUTM1 rearranged porocarcinoma with corresponding immunohistochemical expression: Review of recent advances in poroma and porocarcinoma pathogenesis with potential diagnostic utility.

Porocarcinoma is a rare malignant adnexal tumor with predilection for the lower extremities and the head and neck region of older adults. This entity may arise de novo or in association with a benign poroma. Porocarcinoma's non-specific clinical appearance, immunohistochemical profile, and divergent differentiation may occasionally be diagnostically challenging. Recently, highly recurrent YAP1 and NUTM1 gene rearrangements have been described in cases of poroma and porocarcinoma. In this report, we present a case of porocarcinoma with squamous differentiation in an 81-year-old woman which harbored rearrangement of the YAP1 and NUTM1 loci and was diffusely immunoreactive for NUTM1. We discuss the recent advancements in the pathogenesis of poromas and porocarcinomas with emphasis on the clinical utility of the NUTM1 antibody.

Utility of YAP1 and NUT immunohistochemistry in the diagnosis of porocarcinoma.

BACKGROUND: Porocarcinoma is the malignant counterpart of poroma, a benign tumor derived from the eccrine or apocrine units. In contrast to poroma, porocarcinoma is rare and its diagnosis may be challenging. Recent work has identified YAP1-associated gene fusions in most poromas, and a subset of porocarcinomas. These included YAP1-MAML2 and YAP1-NUTM1, the latter being enriched in porocarcinomas over poromas. METHODS: We studied YAP1 C-terminus and NUT immunohistochemistry in a cohort of 12 porocarcinomas, 10 poromas, 10 squamous cell carcinomas, and 6 hidradenocarcinomas. RESULTS: Seven of 12 (58%) porocarcinomas showed loss of YAP1 C-terminus expression, consistent with a YAP1 fusion. Of these seven, five showed NUT positivity, implying the presence of the YAP1-NUTM1 fusion. One of 12 (8%) cases showed NUT positivity, but retention of YAP1 C-terminus expression, consistent with a non-YAP1 NUT-associated fusion. Eight of 10 (80%) poromas showed loss of YAP1 C-terminus expression and negative NUT staining, consistent with non-NUT YAP1 fusions. All squamous cell carcinomas and hidradenocarcinomas retained YAP1 C-terminus expression and were negative for NUT. CONCLUSION: YAP1 C-terminus and NUT immunohistochemistry may be helpful in the diagnosis of porocarcinoma, with the combination of YAP1 C-terminus loss and NUT positivity being particularly informative.

Poroid adnexal skin tumors with YAP1 fusions exhibit similar histopathologic features: A series of six YAP1-rearranged adnexal skin tumors.

BACKGROUND: Adnexal skin tumors are diagnostically challenging with few known molecular signatures. Recently, however, YAP1-MAML2 and YAP1-NUTM1 fusions were identified in poroid adnexal skin tumors. METHODS: Herein, we subjected eight poroid adnexal skin tumors (three poromas and five porocarcinomas) to fusion gene analysis by whole transcriptome sequencing and next-generation DNA sequencing analysis. RESULTS: YAP1 fusions were identified in six cases. YAP1-NUTM1 fusions were identified in two poromas and three porocarcinomas. A single case of porocarcinoma harbored a YAP1-MAML2 fusion. Two cases were negative for gene fusion. All cases that harbored YAP1-NUTM1 fusions showed nuclear protein in testis (NUT) expression by immunohistochemistry, with NUT being negative in the YAP1-MAML2-positive case. In this case series, we provide a detailed histopathologic description of six YAP1-fused poroid skin tumors, which we show harbor reproducible histopathologic features, to include broad, bulbous tumor tongues with admixtures of basaloid, poroid cells punctuated by squamatized cuticles and ductules, with uniform tumor nuclei featuring frequent grooves and pseudonuclear inclusions. CONCLUSIONS: Awareness of the characteristic histopathologic features of YAP1-fused poroid adnexal skin tumor is a step toward a more reproducible classification of adnexal skin tumors as well as a step toward targeted therapy for metastatic and/or unresectable examples of this poroid group of neoplasms.

Characteristic Clinical and Dermoscopic Features of Nonvolar Poroma.

BACKGROUND: A poroma typically presents as a solitary, pink-to-red papule or nodule in acral volar areas. However, in nonvolar areas, this typical clinical feature (TCF) can be difficult to identify. OBJECTIVE: We aimed to compare clinical and dermoscopic characteristics between nonvolar poroma (NVP) and volar (ie, typical) poroma (VP). METHODS: We assessed the clinical and dermoscopic characteristics of 40 patients with poromas who were divided into the NVP and VP groups. RESULTS: Of the 40 patients, 20 (50.0%) were allocated to the NVP group and 20 (50.0%) to the VP group. Pigmented variants were more common in the NVP group than in the VP group (60.0% vs 5.0%). The TCF of poroma was observed less frequently in the NVP than the VP group (45.0% vs 85.0%). Approximately one-third (30.0%) of patients with NVP received an initial clinical diagnosis of skin cancer. Dermoscopic patterns associated with melanoma or basal cell carcinoma were more common in the NVP group than in the VP group (65% vs 30%). CONCLUSIONS: Skin cancer-associated clinicodermoscopic features were more frequently observed in patients with NVP, who simultaneously lost dermoscopic patterns associated to poromas and acquired those associated with skin cancer, than those with VP.

Eccrine poroma of the eyelid.

Clinical and histopathologic case of an eyelid eccrine poroma, a benign adnexal neoplasm rarely found on the periorbital skin.

Rare case of large eccrine poroma of the eyelid.

Eccrine poroma is a rare tumor arising from sweat glands with common location being soles and palms. We are reporting a case of 70-year male patient with large lower lid mass lesion. Owing to its location and history of growth, malignancy was suspected. Biopsy proved it to be eccrine poroma which is a benign lesion. Complete excision with lid reconstruction was done. Eccrine poroma, though rare, should be kept in the differential diagnosis of eyelid tumors. Owing to the risk of malignant transformation and difficulty in clinical differentiation between poroma and porocarcinoma, wide excision should be done.

Altered Rb, p16, and p53 expression is specific for porocarcinoma relative to poroma.

BACKGROUND: Porocarcinomas are rare aggressive carcinomas that harbor tumor suppressor mutations and must be distinguished from benign entities such as poromas. METHODS: To determine whether altered expression of these genes was diagnostically informative, we examined p53, Rb, and p16 staining patterns in 15 poromas and 16 porocarcinomas. RESULTS: Poromas consistently displayed diffuse strong expression of Rb in all but one case that displayed focal loss (1/15, 7%), and no evidence of aberrancy in p53 or p16. Porocarcinomas displayed diffuse or focal loss of Rb expression in 9/16 (56%) cases, diffuse loss or overexpression of p53 in 8/15 (53%), and diffuse loss or overexpression of p16 in 6/14 (43%). Diffuse aberrancy in p53 and Rb expression correlated with tumor mutations in TP53 and RB1, respectively, whereas focal Rb loss was associated with wild type RB1. Diffuse p16 overexpression correlated with Rb loss rather than CDKN2A mutation. For porocarcinomas with all three stains evaluable, 10/13 (77%) displayed aberrancy in at least one marker. CONCLUSIONS: Our findings suggest that altered p53, p16, and/or Rb expression is relatively specific to porocarcinoma in comparison with poroma. Technical limitations of this panel, including possible focal Rb loss, must be kept in mind, especially in limited samples.

Poromas with large lumens histopathologically mimicking syringocystadenoma papilliferum: Report of three cases.

We report on three patients exhibiting tumours with exophytic pedunculated structures with eroded surfaces. All cases showed the basic histopathological features of poroma accompanied by large, invaginated ductal structures lined by multiple layers of columnar or cuboidal cells. The columnar cells of invaginated ductal/cystic structures focally exhibited subtle features reminiscent of decapitation secretion along with dense infiltration of plasma cells in the surrounding stroma, mimicking syringocystadenoma papilliferum.