Sebaceous Duct Research Articles

Myc-dependent dedifferentiation of Gata6+ epidermal cells resembles reversal of terminal differentiation

Dedifferentiation is the process by which terminally differentiated cells acquire the properties of stem cells. During mouse skin wound healing, the differentiated Gata6-lineage positive cells of the sebaceous duct are able to dedifferentiate. Here we have integrated lineage tracing and single-cell mRNA sequencing to uncover the underlying mechanism. Gata6-lineage positive and negative epidermal stem cells in wounds are transcriptionally indistinguishable. Furthermore, in contrast to reprogramming of induced pluripotent stem cells, the same genes are expressed in the epidermal dedifferentiation and differentiation trajectories, indicating that dedifferentiation does not involve adoption of a new cell state. We demonstrate that dedifferentiation is not only induced by wounding, but also by retinoic acid treatment or mechanical expansion of the epidermis. In all three cases, dedifferentiation is dependent on the master transcription factor c-Myc. Mechanotransduction and actin-cytoskeleton remodelling are key features of dedifferentiation. Our study elucidates the molecular basis of epidermal dedifferentiation, which may be generally applicable to adult tissues.

Reassessing Stephanofilaria stilesi dermatitis in cattle, with characterization of molecular markers for confirming diagnosis

BackgroundStephanofilaria stilesi is a vector-borne filarioid nematode of cattle in North America that is transmitted via the hematophagous horn fly (Haematobia irritans) intermediate host. Despite being relatively common, little attention has been given to a thorough description of S. stilesi lesions and the potential integration of pathological and molecular diagnostic findings to confirm infection.MethodsTo characterize the cutaneous lesions caused by S. stilesi in cattle (Bos taurus taurus and Bos taurus indicus), skin of the ventral abdominal midline was collected from 22 animals during postmortem examination. Skin samples were processed for histology, transmission electron microscopy (TEM), DNA extraction, PCR, and Sanger sequencing targeting molecular markers cytochrome oxidase c subunit 1 (cox1), 12S, 18S rDNA, and 28S rDNA.ResultsMacroscopically, lesions ranged from 5 × 4 cm to 36 × 10 cm, consisting of one large single lesion, or two to four ovoid areas at the ventral abdominal midline, surrounding the umbilicus. Each lesion presented as ulcerative dermatitis with dry, serocellular crusts, or alopecic and lichenified areas. Histologically, eosinophilic, neutrophilic, and ulcerative dermatitis with furunculosis, folliculitis, and epidermal hyperplasia was observed. Cross sections of adult nematodes were identified in ~ 60% of the cases (n = 13) within intact follicles, sebaceous ducts, crusts, and areas of furunculosis. Stephanofilaria first-stage larvae (L1) were observed in five cases within “vitelline membranes” in the superficial dermis and crusts. Ultrastructurally, the L1 cross sections were compounded of smooth multilayered cuticle and somatic cells. The “vitelline membrane” is a tri-layered membrane where L1 are suspended in a matrix. Stephanofilaria stilesi DNA was found in 5 out of the 13 cases in which adults or L1 were histologically observed (38%) and in 1 out of the 9 cases without adults or L1 present (11%). Phylogenetic analyses suggest a closer relationship of the genus Stephanofilaria with Thelazioidea, instead of the family Filariidae (Filarioidea), in which it has been historically allocated.ConclusionsOur study improved the characterization of lesions and described ultrastructural findings of S. stilesi and highlights that molecular tools should be utilized in combination with histology for improved diagnostic resolution.Graphical

DP16 Trichilemmocysticus naevus: a rare birthmark treated successfully with erbium ablative laser

Abstract We report a rare case of a 58-year-old woman with a naevus trichilemmocysticus. The patient presented to a tertiary dermatology centre with longstanding skin changes to her trunk. The changes had been apparent since childhood and became more prominent in her teens. Examination showed a linear Blaschkoid distribution of subtle hyperpigmentation and warty follicular prominence to the left submammary region, extending to the left upper back, where comedones and cystic papules were also noted. Histopathology confirmed the presence of cysts containing keratin, lined by trichilemmal-type squamous epithelium, representing trichilemmal cysts. The overlying epidermis appeared normal. Given the Blaschkoid distribution and the presence since childhood, it was thought that this most likely represented a naevus trichilemmocysticus. Tantcheva-Poor et al. described and named this as a rare type of organoid naevus-type lesion in 2007 (Tantcheva-Poor I, Reinhold K, Krieg T, Happle R. Trichilemmal cyst nevus: a new complex organoid epidermal nevus. J Am Acad Dermatol 2007; 57:S72–7). Only seven cases have been identified and reported in the literature. These have been characterized by multiple follicular filiform hyperkeratoses and trichilemmal cysts in a Blaschkoid distribution. Most cases described involve extensive areas of the skin and present with disfiguring lesions. Histology reports confirm epidermal acanthosis with deep invaginations filled with massive orthokeratosis, parakeratotic columns and an absent granular layer (isthmic or trichilemmal differentiation) with keratosis in sebaceous ducts and acrosyringia. Our patient is currently undergoing successful treatment with erbium laser under local anaesthesia, in order to improve the texture and appearance of the birthmark. This has been achieved by ablation to the warty areas to the level of upper papillary dermis, with focal deeper ablation to the skin overlying each cyst, followed by the use of a meibomian cyst curette for enucleation.

Ocular and extraocular sebaceous carcinomas: A retrospective study with emphasis on the presence of insitu lesion and discussion and review of the histogenesis of extraocular sebaceous carcinoma.

Sebaceous carcinoma (SC) is a rare carcinoma classified as ocular or extraocular. Ocular SC is believed to arise from the meibomian glands or the glands of Zeis. However, the origin of extraocular SC is controversial because there is no evidence of carcinoma arising from pre-existing sebaceous glands. Several hypotheses about the origin of extraocular SC have been proposed, including one suggesting an origin from intraepidermal neoplastic cells. Although extraocular SCs have been shown to occasionally comprise intraepidermal neoplastic cells, no study has investigated whether intraepidermal neoplastic cells possess sebaceous differentiation. The present study analyzed the clinicopathological features of ocular and extraocular SC, with an emphasis on the presence of in situ (intraepithelial) lesions. It retrospectively reviewed the clinicopathological features of eight patients with ocular and three patients with extraocular SC (eight women and three men; median age, 72 years), respectively. In situ (intraepithelial) lesions were observed in four of the eight ocular SC cases and one of the three extraocular SC cases and an apocrine component was noted in one patient with ocular SC (seboapocrine carcinoma). In addition, immunohistochemical analyses showed that the androgen receptor (AR) was expressed in all ocular SCs and two of the three extraocular SC cases. Adipophilin expression was observed in all ocular and extraocular SC. In situ lesions of extraocular SC showed positive immunoreactivity for both AR and adipophilin. The present study is the first to demonstrate sebaceous differentiation in in situ lesions of extraocular SC. The possible origin of extraocular SC is speculated to be the progenitor cells present in the sebaceous duct or interfollicular epidermis. The results of the present study and reported cases of SC in situ indicate that extraocular SC also arises from intraepidermal neoplastic cells.

Ear‐looped face masks associated retro‐auricular abscesses during the COVID‐19 pandemic

AbstractUniversal mask‐wearing has become public‐health recommendations and a necessity in daily life since coronavirus disease 2019 (COVID‐19) pandemic. Accumulating evidence suggests that facial masks may damage the skin. We present a series of six patients with ear‐looped face mask associated retro‐auricular abscesses (RAAs) from a tertiary referral centre, observed between March 2020 and May 2021. Patients’ past medical history included recurrent skin abscess (n = 2), seborrhoeic dermatitis (n = 1) and pre‐existing postauricular cyst (n = 4). All patients reported prolonged use of ear‐looped face masks. Incision and drainage of the abscesses were carried out in all cases, followed by systemic antibiotic treatment. All patients recovered without complications and no recurrences (follow‐up 11−17 months). We hypothesise that ear‐looped face masks may promote the formation of RAAs. Possible mechanisms include local mechanical pressure, friction, changes in the skin's temperature, humidity and microbia, inducing local inflammation and infection, leading to retro‐auricular sebaceous duct obstruction.

Formulation of fig leaf extract (ficus carica L) as an anti-bacterial gel for acne using HPMC base

Acne is a skin disease caused by inflammation, accompanied by blockage of the sebaceous ducts of the skin. One of the causes of acne is Propionibacterium acnes. The purpose of this study is to find out whether the anti-acne gel preparation of fig leaf (Ficus Carica L) can inhibit the growth of P. acnes bacteria and has good physical stability of the preparation.This experimental research started by the preparation of fig leaf extract with 96% ethanol dipping method, and converts it into a gel of 3 formulations with a gelling agent percentage of 2% and a HPMC concentration of 3 n 4%. The evaluation includes stability test and effectiveness test. The well diffusion method is used to inhibit the bacteria of p.acnes, and the stability test is carried out by the accelerated storage method. 10 cycles are 1 cycle, and the time span is 12 hours. The tests performed include sensory tests, uniformity, viscosity, pH, dispersion, viscosity, and syneresis. Data analysis uses a one-way analysis of variance test, followed by post-hock test.The results of this study shows that the physical stability test of Formulation I meets all test requirements except the pH test, and Formulation II and Formulation III meet all test requirements except the viscosity test, spreadability and pH test. In antibacterial test, the antibacterial rate of formula 1 was the highest with 5.3 mm. And the analysis of variance shows that all the formulas are significantly different (p <0.05) Keywords : Formula, gel, acne, tin leaf extract(ficus carica L), Propionibacterium acnes.

Oral Steatocystoma Simplex—A Rare Tumor

Abstract Steatocystoma is a benign adnexal tumor that originates from sebaceous glands or ducts. Steatocystoma simplex presents as a solitary, noninherited tumor that affects adults with equal sex predilection. It can affect any part of the body and is seen most commonly on the skin of the face and neck. Involvement of the oral mucosa is extremely rare. To the best of our knowledge, only 3 intraoral cases have ever been reported. We report a rare case of steatocystoma simplex presented in a 17-year-old male patient involving the buccal mucosa.

TP53 Abnormalities and MMR Preservation in 5 Cases of Proliferating Trichilemmal Tumours.

Proliferating trichilemmal tumours (PTT) are defined by a benign squamous cell proliferation inside a trichilemmal cystic (TC) cavity. A possible explanation of this proliferative phenomenon within the cyst may be molecular alterations in genes associated to cell proliferation, which can be induced by ultraviolet radiation. Among other genes, alterations on TP53 and DNA mismatch repair proteins (MMR) may be involved in the cellular proliferation observed in PTT. Based on this assumption, but also taking into account the close relationship between the sebaceous ducts and the external root sheath where TC develop, a MMR, a p53 expression assessment and a TP53 study were performed in a series of 5 PTT cases, including a giant one. We failed to demonstrate a MMR disorder on studied PTT, but we agree with previous results suggesting increased p53 expression in these tumours, particularly in proliferative areas. TP53 alteration was confirmed with FISH technique, demonstrating TP53 deletion in most cells.

Seborrheic Keratosis With Sebaceous Differentiation, a Series of 8 Cases and Critical Review of the Literature.

Seborrheic keratosis with sebaceous differentiation (SKSD) can sometimes raise uncertainty, confuse with other even malignant entities, and lead to overestimation of this harmless variant. Retrospective analysis of the cases diagnosed as SKSD and a search of the pertaining literature were conducted. Eight cases of SKSD were found. Histologically, these lesions show a flat to plate-like outgrowth of basaloid cells with solitary or clustered sebocytes at the bottom of the rete ridges and variable sebaceous ducts with luminal cuticula. The lesions differed in the outgrowth subpattern: flat/macular, acanthotic, or reticulated. No association was found with Muir-Torre syndrome, and no malignant transformation was seen in these lesions. Literature search revealed confusingly designated lesions that simply represented SKSD. SKSD can show several growth patterns as classic SK. This entity is either underreported or even underrecognized. This entity is benign; however, according to the literature, exclusion of an associating Muir-Torre syndrome should be warranted. The published literature about this lesion is confusing and inconsistent. We suggest the avoidance of confusing terminology and particularly the terminus epithelioma for such lesions.

Topical Transplantation of Bone Marrow Mesenchymal Stem Cells Made Deeper Skin Wounds Regeneration.

Current wound healing models generally employ full-thickness or irregular split wounds. Consequently, assessing the type of healing at varying wound depths and determining the deepest level at which wounds can regenerate has been a challenge. We describe a wound model that allows assessment of the healing process over a continuous gradient of wound depth, from epidermal to full-thickness dermal loss. Further, we investigate whether green fluorescent protein-labeled bone marrow mesenchymal stem cells (BM-MSCs/GFP) transplantation could regenerate deeper wounds that might otherwise lead to scar formation. A wound gradient was created on the back of 120 Sprague Dawley rats, which were randomized into the BM-MSCs/GFP and control group. These were further subdivided into 6 groups where terminal biopsies of the healing wounds were taken at days 1, 3, 5, 7, 14, and 21 post-operatively. At each observed time point, the experimental animals were anesthetized and photographed, and depending on the group, the animals euthanized and skin taken for rapid freezing, haemotoxylin and eosin staining, and vascular endothelial growth factor (VEGF) immunohistochemistry. We found the deepest layer to regenerate in the control group was at the level of the infundibulum apex, while in the BM-MSCs/GFP group this was deeper, at the opening site of sebaceous duct at hair follicle in which had the appearance of normal skin and less wound contraction than the control group (P value less than .05). The expression of VEGF in BM-MSCs/GFP group was higher than that in control group (P value less than .05). The number of vessels increased from 2.5 ± 0.2/phf of control group to 5.0 ± 0.3/phf of BM-MSCs/GFP (P value less than .05). The progressively deepening wound model we described can identify the type of wound repair at increasing depths. Further, topical transplantation of BM-MSCs/GFP significantly improved regeneration of deeper wounds from infundibulum apex (maximum depth of control group regeneration) to the opening site of sebaceous duct at hair follicle level.

INTRA-ORAL SEBACEOUS ADENOMA: A REPORT OF A CASE

Intra-oral sebaceous adenoma (SA) is a rare benign tumor accounting for 0.1% of all salivary gland neoplasms consisting of sebaceous epithelium in a fibrous stroma. A 50-year-old female was referred by her dentist for treatment of an oral lesion in the right buccal mucosa and retromolar trigone. Clinically, a nodule asymptomatic was observed, 1.5 cm, sessile base, rose-colored with the central region yellowish and areas of telangiectasia, with 6 months’ of evolution. The patient also presented Fordyce granules on buccal mucosa, bilaterally. Clinical diagnosis of lipoma was made. After excisional biopsy, the histologic sections revealed a tumor composed of sebaceous cell nests and dilated salivary ducts with areas of squamous differentiation and minimal atypia, enclosed in a fibrous stroma. Minor salivary glands with usual aspects were observed deeply. Final diagnosis was SA, and the patient follow-up is being conducted.

Multiple milia formation in blistering diseases.

BackgroundMilia are superficial keratinous cysts seen as pearly white, dome-shaped lesions 1–2 mm in diameter. Milia are associated with diseases that cause subepidermal blistering, such as hereditary forms of epidermolysis bullosa, epidermolysis bullosa acquisita, bullous pemphigoid, bullous lichen planus, and porphyria cutanea tarda. Multiple eruptive milia are rare and more extensive in number than primary milia.ObjectiveThe aim of this study was to search the literature for cases of blistering diseases with multiple milia formation, especially in areas of the skin where there was no evidence of blistering or trauma, and review the interpretations of their pathogenesis.MethodsWe performed a literature search with the terms multiple milia and bullous diseases, pemphigoid, and pemphigus.ResultsVery few studies have investigated the origin of milia. Primary milia are thought to originate from the sebaceous collar of vellus hairs, and secondary milia are believed to derive from eccrine ducts more commonly than from overlying epidermis, hair follicles, or sebaceous ducts. Milia secondary to blisters or trauma are speculated to be produced through the regeneration process of disrupted sweat glands or hair follicles. Immunological predisposition, aberrant interaction between the hemidesmosomes, and the extracellular matrix components beneath the hemidesmosomes have been described with regard to the formation of numerous milia during recovery. Multiple milia could be a primary manifestation of dystrophic epidermolysis bullosa in skin areas without evidence of blistering.ConclusionThe exact etiology of multiple milia remains unknown. Immunological predisposition and improper interaction between hemidesmosomes and extracellular matrix components are speculated to play a role in the formation of milia during recovery of bullous lesions in blistering diseases. Still, further studies on the triggering mechanisms of keratinocyte dysfunction in cases of multiple milia formation without evidence of prior blistering are needed.

TRICHILEMMAL CYST: A POSSIBLY MALIGNANT RARE INJURY IN UPPER LIP - CASE REPORT

Trichilemmal cyst is rare cyst, with small incidence in mouth, which can affect both sexes; however, is more common in women, having the possibility to become malignant. Its pathogenesis is related to the sebaceous glands ducts obstruction leading to the retention of secretion, being filled by keratin. Its occurrence is more common in hairy regions or close to them. A 54-year-old man arrived with the main complaint of a little ball that moved back and forward in the upper lip. The physical examination reported the presence of nodule measuring 5 mm, which was mobile, painless, and covered with normal mucosa. After image and blood complementary examinations, an excisional biopsy with small safety margin was performed. The anatomopathologic examination result was trichilemmal cyst. The patient remains asymptomatic and without relapse signals. His prognosis is favorable.

Persistent cheek lesion with surrounding clusters

A 50-year-old woman presented with groups of multiple small, round, whitish papules on her cheeks. Biopsy was take from one of the papules. There was no significant prior medical history...

Holocrine Secretion Occurs outside the Tight Junction Barrier in Multicellular Glands: Lessons from Claudin-1–Deficient Mice

Holocrine secretion is a specific mode of secretion involving secretion of entire cytoplasmic materials with remnants of dead cells, as observed in multicellular exocrine glands of reptiles, birds, and mammals. Here, we found that sebaceous glands in mice, representative of multicellular exocrine glands of mammals, exhibit a form of polarized stratified epithelium equipped with tight junctions (TJs), and found that holocrine secretion occurred outside the TJ barriers. Sebaceous glands share characteristics of stratified epithelia with interfollicular epidermis, including basal-layer-restricted cell proliferation, TJ barrier formation at a specific single layer of cells with apico-basolateral plasma membrane polarity, and cell death outside the TJ barrier. Knockout of claudin-1, a transmembrane adhesive protein in TJs, in mice caused leakage of the TJ barrier in sebaceous glands and incomplete degradation of the plasma membrane and nuclei during holocrine secretion. Claudin-1 knockout resulted in the accumulation of incompletely degenerated sebocytes in sebaceous ducts, suggesting that the TJ barrier was necessary for differentiation of holocrine secretion. The redefinition of sebaceous glands as TJ-forming stratified epithelia provides an important framework to understand the molecular mechanism of holocrine secretion.

Hamartome folliculaire basaloïde : étude anatomoclinique

Basaloid follicular hamartoma (BFH) is a rare tumor first described in 1985. It bears clinical and histologic similarities with basal cell carcinoma (BCC), in particular the so-called infundibulocystic form. We performed a single-center clinicopathological study of a series of typical cases of this entity that is occasionally difficult to diagnose. All cases of BFH seen at the Dermatopathology Laboratory of Strasbourg University Hospital were included and analyzed by means of HE staining and Ber-EP4and PHLDA1immunolabelling. Diagnosis was made in the event of basaloid proliferation with anastomosing cords developed from a hair follicle. Clinical data were collected from clinical files. We identified 15cases in 13patients of mean age 44.8years (range: 4to 90) and the sex-ratio was 5/8. Lesions consisted of flesh-colored papules measuring 0.3to 1.2cm in diameter, without any preferential site. Three patients had multiple lesions consisting of several coalescent papules on a breast for one, sparse papules on the back for another, and hundreds of linear unilateral BFHs, associated with osseous abnormalities, characteristic of Happle-Tinschert syndrome, for the third. All tumors were limited to the superficial and mid dermis, with a vertical orientation and connection to the epidermis in 14of the 15patients. In some cases, the outermost cells were basophilic while the central cells were eosinophilic. Peripheral palisading and clefting were frequently observed. Keratin cysts or sebaceous ducts were consistently present, indicating follicular differentiation. Ber-EP4+ cells were restricted to the periphery of the cords and PHLDA1was weakly expressed. BFH is a rare entity that must be differentiated from BCC. It presents as solitary or multiple lesions, either grouped in plaques or with a generalized or linear unilateral distribution. Generalized BFH may be associated with autoimmune diseases and linear unilateral BFH with osseous, dental and cerebral abnormalities in Happle-Tinschert syndrome. It is important to distinguish BFH from BCC to avoid inappropriate aggressive treatment.

Spatial analysis of p63, K5 and K7 defines two groups of progenitor cells that differentially contribute to the maintenance of normal sebaceous glands, extraocular sebaceous carcinoma and benign sebaceous tumors

The histogenesis of extraocular sebaceous carcinomas is - in contrast to ocular sebaceous carcinomas - unclear, and information about the exact cellular architecture of these lesions and even of the normal sebaceous gland is still scarce. This study attempts to elucidate the histogenesis of sebaceous tumors, using multicolor immunofluorescence stainings to analyze 21 cases of sebaceous tumors (six each of extraocular sebaceous carcinoma, sebaceous adenoma and sebaceoma, and three cases of steatocystomas) and eight cases of normal sebaceous glands for p63, several keratins, androgen receptor, adipophilin, epithelial membrane antigen (EMA) and Ki-67. The data of this observational study provide evidence for the existence of two subpopulations of progenitors in normal sebaceous glands: (i) p63+ K5+ progenitors which generate the K10+ luminal cells of sebaceous ducts; and (ii) p63+ K5+ K7+ progenitors which finally generate K7+ adipophilin+ EMA+ sebocytes. Without exception, all types of sebaceous tumors contained p63+ K5+ cells. Furthermore, these tumors showed a cellular hierarchy and differentiation to adipophilin+ and/or EMA+ mature sebocytes and to K10+ ductal cells through intermediary cells. Notably, a considerable number of sebaceous tumors lack the K7 pathway of cell maintenance in the normal sebaceous lobule. Based on our data, we propose a cellular algorithmic model of the hierarchy of normal sebaceous glands and of sebocytic tumors in which p63+ K5+ cells play a major role.

Sebaceous gland abnormalities in fatty acyl CoA reductase 2 (Far2) null mice result in primary cicatricial alopecia.

In a large scale screen for skin, hair, and nail abnormalities in null mice generated by The Jackson Laboratory’s KOMP center, homozygous mutant Far2tm2b(KOMP)Wtsi/2J (hereafter referrred to as Far2-/-) mice were found to develop focal areas of alopecia as they aged. As sebocytes matured in wildtype C57BL/NJ mice they became pale with fine, uniformly sized clear lipid containing vacuoles that were released when sebocytes disintegrated in the duct. By contrast, the Far2-/- null mice had sebocytes that were similar within the gland but become brightly eosinophilic when the cells entered the sebaceous gland duct. As sebocytes disintegrated, their contents did not readily dissipate. Scattered throughout the dermis, and often at the dermal hypodermal fat junction, were dystrophic hair follicles or ruptured follicles with a foreign body granulomatous reaction surrounding free hair shafts (trichogranuloma). The Meibomian and clitoral glands (modified sebaceous glands) of Far2-/- mice showed ducts dilated to various degrees that were associated with mild changes in the sebocytes as seen in the truncal skin. Skin surface lipidomic analysis revealed a lower level of wax esters, cholesterol esters, ceramides, and diacylglycerols compared to wildtype control mice. Similar changes were described in a number of other mouse mutations that affected the sebaceous glands resulting in primary cicatricial alopecia.

Loss of Gata6 causes dilation of the hair follicle canal and sebaceous duct.

The uppermost aspect of the hair follicle, known as the infundibulum or hair canal, provides a passageway for hair shaft egress and sebum secretion. Recent studies have indicated that the infundibulum and sebaceous ducts are lined by molecularly distinct differentiated cells expressing markers including Keratin 79 and Gata6. Here, we ablated Gata6 from the skin and observed dilation of both the hair canal and sebaceous ducts, independent of gender and hair cycle stage. Constitutive loss of Gata6 yielded only a mild delay in depilation-induced entry into anagen, while unperturbed mutant mice possessed overtly normal skin and hair. Furthermore, we noted that Keratin 79 and Gata6 expression and localization did not depend upon each other. Our findings implicate Gata6 in maintaining the upper hair follicle and suggest that regulation of this transcription factor may be compromised in pathologies such as acne or infundibular cystic diseases that are characterized by abnormal expansion of this follicular domain.

Holocrine Poroma: A Distinctive Adnexal Tumor.

There are 36 cases of complex poroid tumors with folliculosebaceous and apocrine differentiation reported in the literature. The authors evaluated 111 poroid tumors including 63 typical eccrine poromas and 48 poroid tumors with folliculosebaceous elements. Folliculosebaceous poroid tumors (FSPT) had basaloid and squamous cells (100%), ducts with steatocystoma-like cuticles and holocrine secretions (89.6%), infundibular follicular structures (66.7%), and entrapped sebocytes (56.3%). No definite apocrine decapitation secretions in FSPT were found. Immunohistochemistry was strongly positive for CK903 and focally positive for CAM5.2, epithelial membrane antigen, and carcinoembryonic antigen. No loss of MLH-1, MSH-2, or MSH-6 mismatch repair proteins was found. FSPT had distinctive features that differentiate them from eccrine poromas including the frequent head and neck locations (62.5% vs. 20.6%, P < 0.01), squamous cytology (100% vs. 1.6%, P < 0.01), more prominent cytoplasmic vacuolization (score 1.4/4.0 vs. 0.3/4.0, P < 0.01), presence of infundibular follicular structures (score 1.2/4.0 vs. 0.03/4.0, P < 0.01), presence of ducts with steatocystoma-like cuticles (89.6% vs. 0.0%, P < 0.01), and less stromal hyalinization (score 1.0/4.0 vs. 2.5/4.0, P < 0.01). The authors propose that FSPT are distinctive benign tumors originating from the sebaceous gland duct and are therefore best categorized as holocrine poroma.