Expanding the phenotypic spectrum of GABRG2 variants: a recurrent GABRG2 missense variant associated with a severe phenotype.

Pathogenic missense and truncating variants in the GABRG2 gene cause a spectrum of epilepsies, from Dravet syndrome to milder simple febrile seizures. In most cases, pathogenic missense variants in the GABRG2 gene segregate with a febrile seizure phenotype. In this case series, we report a recurrent, de novo missense variant (c0.316 G > A; p.A106T) in the GABRG2 gene that was identified in five unrelated individuals. These patients were described to have a more severe phenotype than previously reported for GABRG2 missense variants. Common features include variable early-onset seizures, significant motor and speech delays, intellectual disability, hypotonia, movement disorder, dysmorphic features and vision/ocular issues. Our report further explores a recurrent pathogenic missense variant within the GABRG2 variant family and broadens the spectrum of associated phenotypes for GABRG2-associated disorders.

Assessing copy number from exome sequencing and exome array CGH based on CNV spectrum in a large clinical cohort.

PURPOSE: Detection of copy-number variation (CNV) is important for investigating many genetic disorders. Testing a large clinical cohort by array comparative genomic hybridization provides a deep perspective on the spectrum of pathogenic CNV. In this context, we describe a bioinformatics approach to extract CNV information from whole-exome sequencing and demonstrate its utility in clinical testing. METHODS: Exon-focused arrays and whole-genome chromosomal microarray analysis were used to test 14,228 and 14,000 individuals, respectively. Based on these results, we developed an algorithm to detect deletions/duplications in whole-exome sequencing data and a novel whole-exome array. RESULTS: In the exon array cohort, we observed a positive detection rate of 2.4% (25 duplications, 318 deletions), of which 39% involved one or two exons. Chromosomal microarray analysis identified 3,345 CNVs affecting single genes (18%). We demonstrate that our whole-exome sequencing algorithm resolves CNVs of three or more exons. CONCLUSION: These results demonstrate the clinical utility of single-exon resolution in CNV assays. Our whole-exome sequencing algorithm approaches this resolution but is complemented by a whole-exome array to unambiguously identify intragenic CNVs and single-exon changes. These data illustrate the next advancements in CNV analysis through whole-exome sequencing and whole-exome array.Genet Med 17 8, 623-629.

Forced TR2/TR4 expression in sickle cell disease mice confers enhanced fetal hemoglobin synthesis and alleviated disease phenotypes.

Sickle cell disease (SCD) is a hematologic disorder caused by a missense mutation in the adult ß-globin gene. Higher fetal hemoglobin (HbF) levels in red blood cells of SCD patients have been shown to improve morbidity and mortality. We previously found that nuclear receptors TR2 and TR4 repress expression of the human embryonic ε-globin and fetal γ-globin genes in definitive erythroid cells. Because forced expression of TR2/TR4 in murine adult erythroid cells paradoxically enhanced fetal γ-globin gene expression in transgenic mice, we wished to determine if forced TR2/TR4 expression in a SCD model mouse would result in elevated HbF synthesis and thereby alleviate the disease phenotype. In a "humanized" sickle cell model mouse, forced TR2/TR4 expression increased HbF abundance from 7.6% of total hemoglobin to 18.6%, accompanied by increased hematocrit from 23% to 34% and reticulocyte reduction from 61% to 18%, indicating a significant reduction in hemolysis. Moreover, forced TR2/TR4 expression reduced hepatosplenomegaly and liver parenchymal necrosis and inflammation in SCD mice, indicating alleviation of usual pathophysiological characteristics. This article shows that genetic manipulation of nonglobin proteins, or transcription factors regulating globin gene expression, can ameliorate the disease phenotype in a SCD model animal. This proof-of-concept study demonstrates that modulating TR2/TR4 activity in SCD patients may be a promising therapeutic approach to induce persistent HbF accumulation and for treatment of the disease.

Prospective, longitudinal study of plastic bronchitis cast pathology and responsiveness to tissue plasminogen activator.

Plastic bronchitis (PB) is a rare disease that often occurs in patients with congenital heart disease (CHD) who have undergone staged single-ventricle palliation. It is characterized by the formation of rubbery "casts" in the airways. PB treatment frequently includes inhaled tissue plasminogen activator (tPA). However, the efficacy of tPA to reduce cast burden is unknown. This is further complicated by our lack of knowledge of cast composition. We obtained spontaneously expectorated PB casts from children (n = 4) with CHD and one adult patient with idiopathic PB. Pathological assessment was made from paraffin-preserved samples. Casts were treated with phosphate-buffered saline (PBS) or tPA. Cast response to tPA was assessed by changes in cast weight and the production of fibrin D-dimer. Independent of dose, tPA reduced cast weight compared with PBS-treatment (P = 0.001) and increased D-dimer levels. Histological staining showed that PB casts from all patients were composed of fibrin and contained notable numbers of lymphocytes. Cast composition did not change over time. Collectively, these data support that in our PB patients, casts are composed of fibrin and are responsive to tPA treatment. This makes inhaled tPA a potentially viable option for symptomatic relief of PB while we work to unravel the complexity of PB pathogenesis.

Calcifying pseudoneoplasm of the spine.

Calcifying pseudoneoplasms have been rarely reported to involve the spine. Diagnostically, MRI characteristics have not been well-described. We present the case of a 59-year-old woman with a C8 radiculopathy and history significant for metastatic breast cancer. MRI showed a C7-T1 extradural mass with an isointense signal to the spinal cord on T1- and T2-weighted sequences. Mild peripheral enhancement was also noted. The patient underwent a laminectomy to accomplish resection of the underlying lesion. The mass was firm, tan-colored, and adherent to the adjacent dura. A gross total resection was achieved and, postoperatively, the patient had resolution of her radiculopathy. Pathologic analysis confirmed a calcifying pseudoneoplasm. Calcifying pseudoneoplasms can cause exclusively axial pain or may induce radicular or myelopathic symptoms. The pathogenesis is unclear, although the lesions are usually benign. MRI findings can vary, but typically the lesions are extradural, well-demarcated, and mildly enhance peripherally. Surgical resection, either subtotal or total, is highly successful.

Utility of TTF-1 and Napsin-A in the work-up of malignant effusions.

BACKGROUND: Similar to TTF-1, Napsin-A is recently used increasingly to differentiate between pulmonary adenocarcinoma (P-ADC) and extra-pulmonary adenocarcinoma (EP-ADC). The aim of this study was to compare the performance of TTF-1 and Napsin-A in determining the primary origin of adenocarcinoma in malignant serous effusion. METHODS: Following IRB approval, cellblocks from 139 cases of malignant serous effusions of histologically or clinically determined origin including: 26 P-ADC, 108 EP-ADC, 2 pulmonary squamous cell carcinoma (P-SQC), and 3 pulmonary small cell carcinoma (P-SCC) were retrieved. Each case was stained with Napsin-A and TTF-1 and evaluated for positivity and intensity of staining. RESULTS: Napsin-A and TTF-1 stained positive in 17/26 (65%) and 14/26 (54%) of P-ADC and in 2/108 (1.8%) and 0/108 (0%) of EP-ADC with a PPV of 89 and 100%, respectively. In combination, they positively stained 18/26 (70%) of P-ADC with a PPV of 90%. Out of 9 poorly differentiated P-ADC, 7 (78%) stained positive for Napsin-A, while 4 (45%) were reactive for TTF-1. Both Napsin-A and TTF-1 were negative in P-SQC, while P-SCC reacted positively for TTF-1 in 2/3 (66%) of cases and none for Napsin-A. CONCLUSION: Napsin-A and TTF-1 are both useful markers in distinguishing P-ADC from EP-ADC. However, Napsin-A performed better in poorly differentiated P-ADC and its mimickers. The nuclear staining of TTF-1 is crispier and much easier to interpret than Napsin-A cytoplasmic stain. An antibody panel including TTF-1 and Napsin-A or a dual stain will be very helpful in determining the origin of metastatic adenocarcinoma in serous effusion.

Histopathology of Explanted Lungs From Patients With a Diagnosis of Pulmonary Sarcoidosis.

BACKGROUND: Pathologic features of end-stage pulmonary sarcoidosis (ESPS) are not well defined; anecdotal reports have suggested that ESPS may mimic usual interstitial pneumonia (UIP). We hypothesized that ESPS has distinct histologic features. METHODS: Twelve patients who received a diagnosis of pulmonary sarcoidosis and underwent lung transplantation were included. Control subjects were 10 age- and sex-matched lung transplant patients with UIP. Hematoxylin and eosin-stained tissue sections were examined for the following features: extent/pattern of fibrosis; presence and quantity (per 10 high-power fields) of fibroblast foci and granulomas; distribution and morphology of granulomas; and presence and extent of honeycomb change. Extent of fibrosis and honeycomb change in lung parenchyma was scored as follows: 1 = 1% to 25%; 2 = 26% to 50%; 3 = 51% to 75%; 4 = 76% to 100% of lung parenchyma. RESULTS: Eight of 12 cases demonstrated histologic findings typical of ESPS. All showed well-formed granulomas with associated fibrosis distributed in a distinct lymphangitic fashion. Granulomas were present in hilar or mediastinal lymph nodes from six of six patients with ESPS and none of eight control subjects. The extent of fibrosis, honeycomb change, and fibroblast foci was significantly lower in ESPS cases compared with control cases. Two patients with remote histories of sarcoidosis showed histologic features of diseases other than ESPS (UIP and emphysema) without granulomas. Two patients with atypical clinical findings demonstrated nonnecrotizing granulomas combined with either severe chronic venous hypertension or UIP. CONCLUSIONS: ESPS and UIP have distinct histopathologic features in the lungs. Patients with a pretransplant diagnosis of sarcoidosis may develop other lung diseases that account for their end-stage fibrosis.

Adrenal Lymphangioma Masquerading as a Catecholamine Producing Tumor.

Objective. To report the unusual case of an adrenal lymphangioma presenting in a patient with an adrenal cystic lesion and biochemical testing concerning for pheochromocytoma. The pertinent diagnostic and imaging features of adrenal lymphangiomas are reviewed. Methods. We describe a 59-year-old patient who presented with hyperhidrosis and a 2.2 by 2.2 cm left adrenal nodule. Biochemical evaluation revealed elevated plasma-free normetanephrine, urine normetanephrine, urine vanillylmandelic acid, and urine norepinephrine levels. Elevated plasma norepinephrine levels were not suppressed appropriately with clonidine administration. Results. Given persistent concern for pheochromocytoma, the patient underwent adrenalectomy. The final pathology was consistent with adrenal lymphangioma. Conclusions. Lymphangiomas are benign vascular lesions that can very rarely occur in the adrenal gland. Imaging findings are generally consistent with a cyst but are nonspecific. Excluding malignancy in patients presenting with adrenal cysts can be difficult. Despite its benign nature, the diagnosis of adrenal lymphangioma may ultimately require pathology.

Evaluation of napsin A, TTF-1, p63, p40, and CK5/6 immunohistochemical stains in pulmonary neuroendocrine tumors.

OBJECTIVE: A panel of immunohistochemical (IHC) stains frequently used to subclassify non-small cell lung cancers (NSCLCs) includes napsin A, TTF-1, CK5/6, p40, and p63. The expression profiles of these stains in neuroendocrine tumors have not been systematically evaluated. METHOD: Sixty-eight resected pulmonary neuroendocrine tumors, including 52 typical carcinoids (TCs), eight atypical carcinoids (ACs), seven small cell carcinomas (SCLCs) and one large cell neuroendocrine carcinoma (LCNEC), were stained for napsin A, TTF-1, p63, p40, and CK5/6. Tumors were scored as positive (>1% tumor cells reactive) or negative, and percentage of reactive tumor cells was recorded. RESULTS: Napsin A, p63, p40, and CK5/6 were consistently negative in neuroendocrine tumors. TTF-1 was positive in 17 of 52 TCs, 4 of 8 ACs, 5 of 7 SCLCs, and 0 of 1 LCNECs. CONCLUSION: Pulmonary neuroendocrine tumors have a distinct but nonspecific profile on IHC panel commonly applied to subclassify NSCLCs. They are napsin A-/p40-/p63-/CK5/6-/TTF-1±. Recognizing this profile may have value in separating neuroendocrine tumors from NSCLCs.

PGC-1 coactivator activity is required for murine erythropoiesis.

Peroxisome proliferator-activated receptor gamma (PPARγ) coactivator 1α (PGC-1α) and PGC-1ß have been shown to be intimately involved in the transcriptional regulation of cellular energy metabolism as well as other biological processes, but both coactivator proteins are expressed in many other tissues and organs in which their function is, in essence, unexplored. Here, we found that both PGC-1 proteins are abundantly expressed in maturing erythroid cells. PGC-1α and PGC-1ß compound null mutant (Pgc-1(c)) animals express less ß-like globin mRNAs throughout development; consequently, neonatal Pgc-1(c) mice exhibit growth retardation and profound anemia. Flow cytometry shows that the number of mature erythrocytes is markedly reduced in neonatal Pgc-1(c) pups, indicating that erythropoiesis is severely compromised. Furthermore, hematoxylin and eosin staining revealed necrotic cell death and cell loss in Pgc-1(c) livers and spleen. Chromatin immunoprecipitation studies revealed that both PGC-1α and -1ß, as well as two nuclear receptors, TR2 and TR4, coordinately bind to the various globin gene promoters. In addition, PGC-1α and -1ß can interact with TR4 to potentiate transcriptional activation. These data provide new insights into our understanding of globin gene regulation and raise the interesting possibility that the PGC-1 coactivators can interact with TR4 to elicit differential stage-specific effects on globin gene transcription.

Immunophenotyping and protein profiling of Fontan-associated plastic bronchitis airway casts.

RATIONALE: Plastic bronchitis (PB) is a rare and deadly condition that is characterized by the formation of airway casts. It most frequently occurs in children with underlying congenital heart disease that has been surgically palliated by the Fontan procedure. The Fontan circulation results in above-normal central venous pressure, and it has been hypothesized that the formation of airway casts is due to lymph leak. Knowledge of plastic bronchitis pathogenesis is poor and stems mostly from published case reports. OBJECTIVES: To garner information about cast pathogenesis by characterizing inflammatory cell phenotypes in existing formalin-preserved, paraffin-embedded samples and generating protein and cytokine-chemokine profiles of airway cast homogenates. METHODS: We used immunofluorescence confocal microscopy, state-of-the-science proteomics, and a cytokine array assay to immunophenotype cellular content and to generate protein and cytokine profiles of plastic bronchitis airway casts, respectively. MEASUREMENTS AND MAIN RESULTS: Neutrophils, eosinophils, macrophages, and B lymphocytes were identified in cast samples; there were notably fewer T lymphocytes. Fibrin(ogen) was an abundant protein in the cast proteome. Histone H4 was also abundant, and immunofluorescence microscopy demonstrated it to be mostly extracellular. The cytokine profile of plastic bronchitis casts was proinflammatory. CONCLUSIONS: Plastic bronchitis airway casts from children with Fontan physiology are composed of fibrin and are cellular and inflammatory in nature, providing evidence that their formation cannot be explained simply by lymph leak into the airways. Consequences of cellular necrosis including extracellular histones and the apparent low number of T cells indicate that a derangement in inflammation resolution likely contributes to cast formation.

Napsin A is differentially expressed in sclerosing hemangiomas of the lung.

CONTEXT: Sclerosing hemangiomas (SH) are lung tumors characterized by surface cuboidal cells and round stromal cells. The cell of origin remains controversial, though immunohistochemical and ultrastructural studies suggest primitive respiratory epithelium. Napsin A, a human aspartic proteinase found primarily in type II pneumocytes and alveolar macrophages, is emerging as a helpful immunohistochemical marker in characterizing the origin of lung neoplasms, and may be of use in evaluating SH. OBJECTIVE: To evaluate napsin A immunohistochemical staining in SH to further characterize the cell of origin. DESIGN: Six cases of SH were stained for napsin A, as well as thyroid transcription factor 1 and cytokeratin in selected cases. RESULTS: Surface and round cells were positive for thyroid transcription factor 1 in all cases stained with this marker. Cytokeratins were positive in surface cells in all cases stained with this marker; 2 cases had focal cytokeratin staining in round cells. Round cells had focal napsin A staining in 1 case (17%); surface cells were napsin positive in all cases. CONCLUSIONS: The observation of thyroid transcription factor 1 positivity in both surface and round cells in all SH suggests primitive respiratory epithelium as the cell of origin of SH. Our napsin A findings support this, with positivity in surface cells of all tumors (100%), and focal round cell staining in only 1 (17%). In fact, surface cells may represent entrapped type II pneumocytes, which normally express napsin A in a granular cytoplasmic pattern, similar to surface cells. The coexpression of thyroid transcription factor 1 and napsin A also introduces a caveat in differentiating primary pulmonary adenocarcinomas from SH in small biopsy specimens.

Interaction of lipocalin 2, transferrin, and siderophores determines the replicative niche of Klebsiella pneumoniae during pneumonia.

UNLABELLED: Pathogenic bacteria require iron for replication within their host. Klebsiella pneumoniae and other Gram-negative pathogens produce the prototypical siderophore enterobactin (Ent) to scavenge iron in vivo. In response, mucosal surfaces secrete lipocalin 2 (Lcn2), an innate immune protein that binds Ent to disrupt bacterial iron acquisition and promote acute inflammation during colonization. A subset of K. pneumoniae isolates attempt to evade Lcn2 by producing glycosylated Ent (Gly-Ent, salmochelin) or the alternative siderophore yersiniabactin (Ybt). However, these siderophores are not functionally equivalent and differ in their abilities to promote growth in the upper respiratory tract, lungs, and serum. To understand how Lcn2 exploits functional differences between siderophores, isogenic mutants of an Ent(+) Gly-Ent(+) Ybt(+) K. pneumoniae strain were inoculated into Lcn2(+/+) and Lcn2(-/-) mice, and the pattern of pneumonia was examined. Lcn2 effectively protected against the iroA ybtS mutant (Ent(+) Gly-Ent(-) Ybt(-)). Lcn2(+/+) mice had small foci of pneumonia, whereas Lcn2(-/-) mice had many bacteria in the perivascular space. The entB mutant (Ent(-) Ybt(+) Gly-Ent(-)) caused moderate bronchopneumonia but did not invade the transferrin-containing perivascular space. Accordingly, transferrin blocked Ybt-dependent growth in vitro. The wild type and the iroA mutant, which both produce Ent and Ybt, had a mixed phenotype, causing a moderate bronchopneumonia in Lcn2(+/+) mice and perivascular overgrowth in Lcn2(-/-) mice. Together, these data indicate that Lcn2, in combination with transferrin, confines K. pneumoniae to the airways and prevents invasion into tissue containing the pulmonary vasculature. IMPORTANCE: Gram-negative bacteria are a common cause of severe hospital-acquired infections. To cause disease, they must obtain iron and secrete the small molecule enterobactin to do so. Animal models of pneumonia using Klebsiella pneumoniae indicate that enterobactin promotes severe disease. Accordingly, the host defense protein lipocalin 2 exploits this common target by binding enterobactin and disrupting its function. However, pathogenic bacteria often make additional siderophores that lipocalin 2 cannot bind, such as yersiniabactin, which could make this host defense ineffective. This work compares the pattern and severity of pneumonia caused by K. pneumoniae based on which siderophores it produces. The results indicate that enterobactin promotes growth around blood vessels that are rich in the iron-binding protein transferrin, but yersiniabactin does not. Together, transferrin and lipocalin 2 protect this space against all types of K. pneumoniae tested. Therefore, the ability to acquire iron determines where bacteria can grow in the lung.

The application and diagnostic utility of immunocytochemistry on direct smears in the diagnosis of pulmonary adenocarcinoma and squamous cell carcinoma.

The importance of subclassifying pulmonary nonsmall cell carcinoma (NSCLC) in cytologic material is becoming increasingly paramount. Occasionally, cell blocks traditionally used for ancillary studies are sparsely cellular or acellular. Hence, we investigated the diagnostic utility of immunocytochemistry for Napsin-A, TTF-1, and p63 on direct smears of NSCLC. Immunohistochemistry for Napsin-A was initially tested on a tissue microarray (TMA) composed of pulmonary adenocarcinoma. Subsequently, in 25 cases, immunocytochemistry for Napsin-A, TTF-1, and p63 was performed on cytologic direct smears. Smears were prepared from tumor cells scraped from lung resection specimens (n = 10), endobronchial ultrasound-guided transbronchial fine-needle aspirates (n = 13), and pelleted cell material from pleural effusions (n = 2). Immunohistochemistry utilizing the TMA revealed Napsin-A positivity in 73% of pulmonary ADCs. Next, immunocytochemistry on direct cytologic smears demonstrated a Napsin-A(+)/TTF-1(+) immunophenotype in 15 of 18 adenocarcinomas; p63 was completely negative (n = 12) or only focally positive (n = 3) in these 15 adenocarcinomas. The remaining three adenocarcinomas were negative for all three markers. All six squamous cell carcinomas were Napsin-A(-)/TTF-1(-) and diffusely p63(+). In conclusion, direct smears represent a feasible and robust source of cellular material for immunocytochemical studies to diagnose pulmonary ADC and SQC. Our method allows the cytologist to confirm on site that material for diagnostic immunocytochemistry is present thereby serving as a safeguard in instances where the cell block is of insufficient cellularity.

The application of molecular diagnostic studies interrogating EGFR and KRAS mutations to stained cytologic smears of lung carcinoma.

EGFR and KRAS mutation analyses are of increasing importance for guiding the treatment of non-small cell lung carcinomas. Insufficient cellularity of cell blocks can represent an impediment to the performance of these tests. We investigated the usefulness of cytologic direct smears as an alternative specimen source for mutation testing. Tumor cell-enriched areas from freshly prepared and archived rapid Romanowsky-stained direct smears in 33 cases of lung carcinoma were microdissected for DNA isolation and evaluated for EGFR and KRAS mutations. EGFR mutations were detected in 3 adenocarcinomas; 2 tumors had the L858R substitution and 1 an exon 19 deletion. KRAS mutations affecting codon 12, 13, or 61 were detected in 11 cases (8 adenocarcinomas and 3 non-small cell carcinomas). EGFR and KRAS mutations were mutually exclusive. Hence, archived and freshly prepared direct smears represent a robust and valuable specimen source for molecular studies, especially when cell blocks exhibit insufficient cellularity.

Analysis of the lung microbiome in the "healthy" smoker and in COPD.

Although culture-independent techniques have shown that the lungs are not sterile, little is known about the lung microbiome in chronic obstructive pulmonary disease (COPD). We used pyrosequencing of 16S amplicons to analyze the lung microbiome in two ways: first, using bronchoalveolar lavage (BAL) to sample the distal bronchi and air-spaces; and second, by examining multiple discrete tissue sites in the lungs of six subjects removed at the time of transplantation. We performed BAL on three never-smokers (NS) with normal spirometry, seven smokers with normal spirometry ("healthy smokers", HS), and four subjects with COPD (CS). Bacterial 16 s sequences were found in all subjects, without significant quantitative differences between groups. Both taxonomy-based and taxonomy-independent approaches disclosed heterogeneity in the bacterial communities between HS subjects that was similar to that seen in healthy NS and two mild COPD patients. The moderate and severe COPD patients had very limited community diversity, which was also noted in 28% of the healthy subjects. Both approaches revealed extensive membership overlap between the bacterial communities of the three study groups. No genera were common within a group but unique across groups. Our data suggests the existence of a core pulmonary bacterial microbiome that includes Pseudomonas, Streptococcus, Prevotella, Fusobacterium, Haemophilus, Veillonella, and Porphyromonas. Most strikingly, there were significant micro-anatomic differences in bacterial communities within the same lung of subjects with advanced COPD. These studies are further demonstration of the pulmonary microbiome and highlight global and micro-anatomic changes in these bacterial communities in severe COPD patients.

Bronchioloalveolar carcinoma and the significance of invasion: predicting biologic behavior.

A resected adenocarcinoma illustrates challenges in diagnosing bronchioloalveolar carcinoma (BAC). Bronchioloalveolar carcinoma is defined by lack of invasion, something that may be difficult to assess in scars. Small (≤0.5 cm) invasive foci have little impact on the good prognosis associated with low-stage tumors. The term microinvasive adenocarcinoma or minimally invasive adenocarcinoma has been proposed for otherwise typical BACs and small invasive foci measuring 0.5 cm or less. Larger areas of invasion are associated with a more aggressive course and more reliably distinguish BAC from other variants of adenocarcinoma. Separating BAC from other forms of adenocarcinoma is important owing to differences in prognosis and emerging therapeutic strategies.

Cutaneous adnexal differentiation and stromal metaplasia in palate pleomorphic adenomas: a potential diagnostic pitfall that may be mistaken for malignancy.

Cutaneous adnexal differentiation is well-recognized in benign mixed tumors occurring in cutaneous sites. The incidence of this histologic finding in salivary gland sites is not known. We sought to describe the incidence of cutaneous adnexal differentiation in benign mixed tumors of the palate, lip, and parotid gland. Benign mixed tumors of the palate (n=30), lip (n=13), and parotid gland (n=37) resected between 1980 and 2009 at a single academic medical institution were reviewed. All hematoxylin and eosin-stained sections containing neoplasm were reviewed by all authors including one dermatopathologist (S.H.O.). After confirming the diagnosis of benign mixed tumor, we evaluated for morphologic evidence of cutaneous adnexal differentiation and metaplastic epithelial and stromal changes. Chart review was conducted to obtain pertinent clinical information. Cutaneous adnexal differentiation was seen in 20% of palate and 39% of lip benign mixed tumors but in no parotid tumors. The most frequent features of cutaneous adnexal differentiation were tricholemmal differentiation (20% of palate and 39% of lip tumors), infundibulocystic structures (17% and 31%), and trichohyalin granules (13% and 31%). Sebaceous differentiation was seen in only one palate tumor. Varying amounts of stromal adipose were seen in 62, 37, and 22% of lip, palate, and parotid tumors. Osseous metaplasia was seen in one tumor from each site. When cutaneous adnexal differentiation occurs in salivary gland pleomorphic adenomas, it can present a diagnostic pitfall that must not be misinterpreted as carcinoma at biopsy, fine needle aspiration, or frozen section.