Correlation of older age with better progression-free survival despite less aggressive resection in nonfunctioning pituitary adenomas.

OBJECTIVE: Nonfunctioning pituitary adenomas (NFPAs) present at a wide range of ages; it is possible that variable outcomes are based on patient age at presentation. This study aimed to explore long-term outcomes of patients with NFPAs following endonasal transsphenoidal surgery (ETS), considering age stratification. METHODS: This retrospective study included 228 patients with NFPAs who underwent ETS, with a median follow-up period of 63 months. The outcomes included progression-free survival (PFS) rates and neurological and endocrinological outcomes. Age-stratified Kaplan-Meier and Cox proportional hazards analyses were performed. Patients were classified into four age groups: ≤ 49, 50-59, 60-69, and ≥ 70 years. RESULTS: Age-stratified analysis showed a significant correlation between age and PFS in NFPAs (5-year PFS rates: 63.0% in those ≤ 49 years, 76.7% in those 50-59 years, 85.0% in those 60-69 years, and 88.1% in those ≥ 70 years; p = 0.001, log-rank test). Bivariate (HR 1.03, 95% CI 1.01-1.05; p = 0.001) and multivariable (HR 1.03, 95% CI 1.02-1.05; p = 0.001) analyses demonstrated that older age was significantly associated with longer PFS. Multivariable analysis also demonstrated that smaller maximum tumor diameter (HR 0.77, 95% CI 0.60-0.99; p = 0.036) and gross-total resection (HR 8.55, 95% CI 3.90-18.75; p = 0.001) were significantly associated with longer PFS. Multivariable logistic regression analysis demonstrated that only younger age was associated with postoperative improvement of male hypogonadism (HR 0.91, 95% CI 0.84-0.99; p = 0.019). Other postoperative neurological and endocrinological outcomes were not significantly associated with age. CONCLUSIONS: Older patients with NFPAs treated with ETS demonstrated a longer PFS. Of endocrinological outcomes studied, only male hypogonadism improvement was associated with younger patient age.

Long-term outcomes among adults with Langerhans cell histiocytosis.

Advances in the treatment of Langerhans cell histiocytosis (LCH) have resulted in a growing survivor population. There is a lack of data on long-term outcomes among adults with LCH. We conducted a retrospective record review of 219 adults (aged ≥18 years) with LCH. Most common presentation was multisystem (34.2%), followed by single-system pulmonary (32%), unifocal (28.3%), and single-system multifocal (5.5%) LCH. Risk organ involvement (the liver, spleen, or bone marrow) was seen in 8.7% of cases, and 40 of 88 (45.5%) tested cases were BRAFV600E. At a median follow-up of 74 months, 5-year progression-free survival (PFS) was 58.3% and estimated median PFS was 83 months. Median overall survival (OS) was not reached; 5- and 10-year OS rates were 88.7% and 74.5%, respectively. Risk organ involvement was associated with worse PFS (hazard ratio [HR], 4.5) and OS (HR, 10.8). BRAFV600E was not associated with risk organ involvement or survival. When compared with matched unaffected US population, individuals with LCH had a significantly higher risk of overall mortality (standardized mortality ratio [SMR], 2.66), specifically among those aged <55 years at diagnosis (SMR, 5.94) and those with multisystem disease (SMR, 4.12). Second cancers occurred in 16.4% cases, including diverse hematologic and solid organ malignancies. LCH-associated deaths constituted 36.1% of deaths and occurred within 5 years of diagnosis. After 5 years, non-LCH causes of death, including second cancers, chronic obstructive pulmonary disease, and cardiovascular diseases, predominated. Our study highlights, to our knowledge, for the first time, that adults with LCH experience early and late mortality from non-LCH causes and the need for development of targeted survivorship programs to improve outcomes.

A 64-year-Old patient assigned male at birth with COPD and worsening dyspnea while on estrogen and antiandrogen agents.

Among patients with COPD, ventilatory inefficiency in response to exercise can be due to respiratory muscle dysfunction or expiratory flow limitation causing air-trapping and dynamic hyperinflation. We discuss a case of severe ventilatory limitation in response to exercise due to reduced respiratory muscle mass in the setting of gender-affirming hormone therapy (GAHT), and how the interpretation of pulmonary function testing (PFT) and respiratory symptoms among transgender and gender diverse (TGD) patients can be influenced by GAHT.

Neurological Manifestations of Histiocytic Disorders.

PURPOSE OF REVIEW: Histiocytic disorders, including Erdheim-Chester disease (ECD), Langerhans cell histiocytosis (LCH), and Rosai-Dorfman disease (RDD), are rare neoplasms that may present with a spectrum of neurologic involvement. Diagnostic delay is common due to heterogeneity in presentation and challenging pathology. RECENT FINDINGS: Recent advances in the treatment of these diseases targeted towards mutations in the MAP kinase pathway have led to an improved prognosis in these patients with neurologic involvement. It is critical for clinicians to have a high index of suspicion to allow for early targeted treatment and optimize neurologic outcomes. A systematic approach to diagnosis is presented in this article to allow for accurate diagnosis of these rare diseases.

Comparison of the Subcutaneous and Intramuscular Estradiol Regimens as Part of Gender-Affirming Hormone Therapy.

OBJECTIVE: Gender-affirming hormone therapy guidelines describe the estradiol (E2) doses for intramuscular (IM), but not subcutaneous (SC), routes. The objective was to compare the SC and IM E2 doses and hormone levels in transgender and gender diverse individuals. METHODS: This is a retrospective cohort study at a single-site tertiary care referral center. Patients were transgender and gender diverse individuals who received injectable E2 with at least 2 E2 measurements. The main outcomes were the dose and serum hormone levels between the SC and IM routes. RESULTS: There were no statistically significant differences in age, body mass index, or antiandrogen use between patients on SC (n = 74) and those on IM (n = 56). The weekly doses of SC E2, 3.75 mg (IQR, 3-4 mg), were statistically significantly lower than those of IM E2, 4 mg (IQR, 3-5.15 mg) (P =.005); however, the E2 levels achieved were not significantly different (P =.69), and the testosterone levels were in the cisgender female range and not significantly different between routes (P =.92). Subgroup analysis demonstrated significantly higher doses in the IM group when the E2 and testosterone levels were >100 pg/mL and <50 ng/dL, respectively, with the presence of the gonads or use of antiandrogens. Multiple regression analysis demonstrated that the dose was significantly associated with the E2 levels after adjusting for injection route, body mass index, antiandrogen use, and gonadectomy status. CONCLUSION: Both the SC and IM E2 achieve therapeutic E2 levels without a significant difference in the dose (3.75 vs 4 mg). SC may achieve therapeutic levels at lower doses than IM .

Ophthalmologic Involvement in Adults with Histiocytic Disorders: Clinical Presentation and Treatment Outcomes.

PURPOSE: To evaluate the clinical presentation, treatment, and outcomes in adult patients with histiocytic disorders with ocular, orbital, optic nerve, or cavernous sinus involvement. DESIGN: Observational, retrospective chart review. PARTICIPANTS: Adult patients (age ≥ 18 years) at Mayo Clinic from January 1, 1996, to July 1, 2021, with histiocytic disorders. Inclusion criteria were (1) histiocytic disorder by biopsy and appropriate clinical phenotype; (2) available medical records; and (3) ocular, orbital, optic nerve, or cavernous sinus involvement. METHODS: Retrospective chart review. MAIN OUTCOME MEASURES: Response to therapy, measured in clinical and radiographic impact. RESULTS: Thirty-two patients were identified: 7 with Langerhans cell histiocytosis (LCH); 15 with Erdheim-Chester disease (ECD); 1 with mixed LCH/ECD phenotype; 8 with Rosai-Dorfman disease (RDD); and 1 with mixed RDD/ECD phenotype. Ophthalmologic involvement was part of the initial presentation in 69% of patients (22/32). Eyelid edema (13/32, 41%) and proptosis (12/32, 38%) were the most frequent presentations. Isolated orbital or cavernous sinus involvement was present in 3 of 7 patients with LCH and 1 of 8 patients with RDD. Optic nerve sheath involvement was present in 2 of 7 LCH patients, 14 of 15 ECD patients, and 1 RDD/ECD patient. Diffuse (> 75%) orbital involvement was seen in 12 of 15 ECD patients and 1 of 7 LCH patients. Ocular involvement was seen in 1 of 15 ECD patients, 6 of 8 RDD patients, and 1 of 1 mixed RDD/ECD patient. The cavernous sinuses were involved in 1 of 7 LCH patients, 5 of 15 ECD patients, and both mixed phenotype patients. Visual acuity was affected in 14 patients (14/24, 58%) with a median logarithm of the minimum angle of resolution visual acuity of 0.1 (range, -0.12 to 3). BRAF V600E mutations were found in 75% (3/4) of LCH patients and 91% (10/11) of ECD patients. Patients received a variety of treatment, and response was variable across disease types. CONCLUSIONS: Orbital involvement was more commonly seen in LCH and ECD, whereas ocular involvement was more common in RDD. Visual acuity may be impacted from ocular involvement or compression of the optic nerve with diffuse orbital involvement.

Outcomes After Treatment With Cobimetinib in Patients With Rosai-Dorfman Disease Based on KRAS and MEK Alteration Status.

Importance: Rosai-Dorfman disease (RDD) is a rare histiocytic neoplasm with recent studies showing alterations in the MAPK pathway, most commonly in the KRAS and MEK genes in about 40% of patients. Reports on the use of MEK-inhibitor therapy in RDD have been limited to small case studies. There are no approved treatments for this neoplasm, and therefore patients with RDD need efficacious treatments. Objective: To study the outcomes after treatment with cobimetinib based on MAPK pathway alterations in patients with RDD. Design, Setting, and Participants: This retrospective cohort study conducted at 2 tertiary care centers included patients with RDD who underwent treatment with cobimetinib between January 1, 2013, and December 1, 2021. Cobimetinib was administered at a dosage of 20 to 60 mg orally once daily as a single agent for 21 days in a 28-day cycle. Pathology was centrally reviewed. Response assessment was centrally conducted and was based on the established positron emission radiography response criteria used for clinical trials of targeted therapies in histiocytosis. Main Outcomes and Measures: Main outcomes were overall response rate (ORR), progression-free survival (PFS), adverse events (AEs) of cobimetinib in the entire cohort, and ORRs and PFS based on MAPK pathway alterations in patients with RDD. Results: A total of 16 patients (median [range] age at cobimetinib initiation, 57 [31-74] years; 11 [69%] women) were included in the study. The median follow-up duration was 19.0 months (95% CI, 8.4-27.8 months). The ORR was 63% (n = 10), including 5 complete responses and 5 partial responses. Somatic alterations in the KRAS or MEK genes were detected in 8 (50%) patients. Patients with KRAS or MEK alterations had significantly higher ORR (88% vs 38%; P = .03), deeper responses (complete responses among responders: 71% vs 0%; P = .002), and better PFS (at 1 year, 100% vs 29% were free from progression or death, respectively; P < .001) compared with those without such alterations. Grade 2 or higher AEs occurred in 12 (75%) patients, and 9 (56%) required dose reduction or temporary/permanent treatment discontinuation due to AEs. Conclusions and Relevance: In this cohort study, treatment with cobimetinib was associated with positive outcomes in KRAS- or MEK-variant RDD. However, AEs requiring dose modifications were common.

Impact of a Multidisciplinary Tumor Board on the Care of Patients with Histiocytic Disorders: The Histiocytosis Working Group experience.

INTRODUCTION: Histiocytic disorders pose significant diagnostic and management challenges for the clinicians due to diverse clinical manifestations and often non-specific histopathologic findings. Herein, we report the tumor board experience from the first-of-its-kind Histiocytosis Working Group (HWG). MATERIALS AND METHODS: The HWG was established in June 2017 and consists of experts from 10 subspecialties that discuss cases in a multidisciplinary format. We present the outcome of tumor board case discussions during the first 2 years since its inception (June 2017-June 2019). RESULTS: Forty cases with a suspected histiocytic disorder were reviewed at HWG during this time period. Average number of subspecialties involved in HWG case discussion was 5 (range, 2-9). Histiocytosis Working Group tumor board recommendations led to significant changes in the care of 24 (60%) patients. These included change in diagnosis (n = 11, 27%) and change in treatment (n = 13, 33%). CONCLUSION: Our report highlights the feasibility of a multidisciplinary tumor board and its impact on outcomes of patients with histiocytic disorders.

Sustained, complete response to pexidartinib in a patient with CSF1R-mutated Erdheim-Chester disease.

Erdheim-Chester disease (ECD) is a histiocytic neoplasm that predominantly harbors mitogen-activated protein kinase (MAPK) pathway variants. MAPK inhibitors typically are effective treatments, but mutations outside the MAPK pathway, such as CSF1R variants, may cause refractory ECD. We describe a patient with a novel somatic mutation in CSF1R (CSF1RR549_E554delinsQ ) that resulted in refractory ECD affecting the central nervous system. Cell model studies, RNA sequencing analysis, and in silico protein modeling suggested that she had a gain-of-function mutation occurring in a region critical for autoinhibition. The patient was treated with pexidartinib, a CSF1R inhibitor, and has had a complete clinical and metabolic response lasting more than 1.5 years to date. To our knowledge, this is the first report to describe successful treatment of a patient with ECD by using an agent that specifically targets CSF1R. This case also highlights the critical role of individualized molecular profiling to identify novel therapeutic targets in ECD.

Mimics of Erdheim-Chester disease.

Erdheim-Chester disease (ECD) is a rare histiocytic neoplasm with frequent multiorgan involvement. An accurate diagnosis of ECD requires the correlation of clinical features, histopathologic and radiologic findings. We describe a case series of patients with a referral diagnosis of ECD, whereby the diagnosis was changed to non-histiocytic diseases after comprehensive review at a tertiary care center. This accurate revision of the referral diagnosis of ECD enabled initiation of proper disease-directed therapy in a timely manner for these patients and avoided unnecessary exposure to systemic cytotoxic chemotherapy or targeted agents. Our study highlights the value of a multidisciplinary team of histiocytosis experts in confirming the diagnosis of ECD and also brings attention to other conditions to consider that can mimic ECD, including osteopoikilosis, tenosynovial giant cell tumour, IgG4-related disease, fibrous dysplasia and chronic recurrent multifocal osteomyelitis.

Characteristics of Transgender Women Referred to Women's Heart Clinic.

INTRODUCTION: Transgender women have been reported to have a high burden of cardiovascular disease (CVD) and risk factors based largely on surveys. Our aim was to describe the prevalence of CVD and associated comorbidities among a cohort of older transgender women referred to cardiology as part of their gender-affirming care. METHODS: This was a retrospective, cross-sectional study of transgender women at a single institution from 2017 to 2019. RESULTS: Fifty-two consecutive patients were included. The most common reasons for referral were cardiac risk factor management (45%) and pre-operative cardiac risk stratification prior to gender-affirming surgery (35%). The mean age was 57 ± 10 years, 87% were white, and 92% had insurance coverage. Forty-eight patients (92%) were taking gender-affirming hormone therapy; 5 had undergone breast augmentation, 4 had undergone orchiectomy, and 2 had undergone vaginoplasty. The most common comorbidities were depression and/or anxiety (63%), obesity (58%), and hyperlipidemia (54%). Excluding aldosterone antagonists, 46% were on cardiac medications; changes were recommended for 25% of patients: new prescriptions in 9, dose adjustments in 5, and discontinuations in 4. According to the pooled cohort equation, the 10-year risk of atherosclerotic CVD was 9.4 ± 7.7% when the study population was calculated as male and 5.2 ± 5.1% when calculated as female (p <0.001). For patients who completed exercise testing, the functional aerobic capacity was fair (77.6 ± 21.4%) when calculated as male and average (99.5 ± 27.5%) as female (p < .0001); there was inconsistency in sex used for calculating the result on the formal report. CONCLUSIONS: Older transgender women may have an underestimated prevalence of CVD and its risk factors. More research is needed to identify cardiovascular health profiles, improve practice consistency, and establish normative values for transgender patients.

Pituitary Tumor Surgery: Comparison of Endoscopic and Microscopic Techniques at a Single Center.

OBJECTIVE: To understand the transition from microscopic surgery (MS) to endoscopic surgery (ES) on the pituitary across the United States, we assessed a single institution practicing both procedures to discern advantages and disadvantages for each. PATIENTS AND METHODS: Retrospective institutional chart review of 534 patients in a large practice over a 6-year period (January 1, 2014, to December 31, 2019) comparing a single MS neurosurgeon with a single ES neurosurgeon operating on the same days. RESULTS: In this series, 14% (n=75) of patients had a prior operation, there were no carotid artery injuries, the overall risk for a postoperative infection was 0.4% (n=2), and risk for a postoperative cerebrospinal fluid leak requiring treatment was 2.0% (n=11). Mean ± SD hospital stay was 1.3±0.04 days; readmission for any reason within 30 days occurred in 3.4% (n=18) of patients. The mean volumetric resection for MS was 86.9%±1.7% and for ES was 91.7%±1.3% (P=.03). There was a higher rate of notable events (P=.015) with MS, but MS had 16% lower cost and operative times were 48 minutes shorter than for ES (83±7 vs 131±6 minutes). The ES required substantially fewer postoperative secondary treatments such as radiation therapy (P=.003). CONCLUSION: Pituitary surgery is a very safe and effective procedure regardless of technique. The MS has shorter operative times and overall lower cost. The ES results in increased volumetric resection and fewer secondary treatments. Both techniques can be valuable to a large practice, and understanding these niches is important when selecting optimal approaches to pituitary surgery for a given patient.

A Comprehensive Study of Spindle Cell Oncocytoma of the Pituitary Gland: Series of 6 Cases and Meta-Analysis of 85 Cases.

OBJECTIVE: To discuss optimal treatment strategy for spindle cell oncocytoma (SCO) of the pituitary gland. METHODS: Institutional cases were retrospectively reviewed. A systematic literature search and subsequent quantitative synthesis were performed for further analysis. The detailed features were summarized and the tumor control rate (TCR) was calculated. RESULTS: Eighty-five patients (6 institutional and 79 literature) were included. The annual incidence was approximately 0.01-0.03/100,000. The mean age was 56 years. Vision loss was present in 60%. Seventy-three percent showed hormonal abnormalities. On magnetic resonance imaging, tumor was avidly enhancing, and the normal gland was commonly displaced anterosuperiorly. Evidence of hypervascularity was seen in 77%. Gross total resection (GTR) was achieved in only 24% because of its hypervascular, fibrous, and adhesive nature. The mean postoperative follow-up was 3.3 years for institutional cases and 2.3 years for the integrated cohort. The TCR was significantly better after GTR (5-year TCR, 75%; P = 0.012) and marginally better after non-GTR + upfront radiotherapy (5-year TCR, 76%; P = 0.103) than after non-GTR alone (5-year TCR, 24%). The TCRs for those with low Ki-67 index (≤5%) were marginally better than those with higher Ki-67 index (5-year rate, 57% vs. 23%; P = 0.110). CONCLUSIONS: Frequent endocrine-related symptoms, hypervascular signs, and anterosuperior displacement of the gland support preoperative diagnosis of SCO. GTR seems to have better long-term tumor control, whereas the fibrous, hypervascular, and adhesive nature of SCO makes it difficult to achieve GTR. In patients with non-GTR, radiotherapy may help decrease tumor progression.

A community-based study of demographics, medical and psychiatric conditions, and gender dysphoria/incongruence treatment in transgender/gender diverse individuals.

BACKGROUND: Current understanding about health care in the gender diverse population is limited by the lack of community-based, longitudinal data, especially in the USA. We sought to characterize a community-based cohort of transgender individuals including demographics, gender identities, social characteristics, psychiatric and medical conditions, and medical therapy for gender dysphoria/incongruence. PATIENTS AND METHODS: We performed a retrospective chart review of gender diverse residents of Olmsted County, Minnesota, who sought gender-specific healthcare from January 1, 1974, through December 31, 2015, using an infrastructure that links medical records of Olmsted County residents from multiple institutions. RESULTS: The number of patients seeking gender-specific healthcare increased from 1 to 2 per 5-year interval during the 1970s-1990s to 41 from 2011 to 2015 (n = 82). Forty-nine (59.8%) were assigned male sex at birth (AMAB), 31 (37.8%) were assigned female (AFAB), and 2 (2.4%) were intersex. Gender identities evolved over time in 16.3% and 16.1% of patients AMAB and AFAB, respectively, and at most recent follow-up, 8.2% and 12.9% of patients AMAB and AFAB, respectively, were non-binary. Depression affected 78%, followed by anxiety (62.2%), personality disorder (22%), and post-traumatic stress disorder (14.6%). 58.5% experienced suicidal ideation, 22% attempted suicide, and 36.6% were victims of abuse. The most prevalent medical conditions and cardiovascular (CV) risk factors included obesity (42.7%), tobacco use (40.2%), fracture [34.1% (86.2% traumatic)], hypertension (25.6%), hyperlipidemia (25.6%), and hypertriglyceridemia (15.9%). 67.3% of patients AMAB used feminizing and 48.4% of patients AFAB used masculinizing hormone therapy. When compared to US CDC National Health Statistics, there was a significantly greater prevalence of depression and anxiety but no difference in the prevalence of obesity, hypertension, hypercholesterolemia, type 2 diabetes, or stroke. CONCLUSION: Transgender and gender diverse individuals represent a population who express various gender identities and are seeking gender-specific healthcare at increasing rates. Psychiatric illness is highly prevalent compared to the US population but there is no difference in the prevalence of CV risk factors including obesity, type 2 diabetes, hypertension, and dyslipidemia.

Urine steroid metabolomics for the differential diagnosis of adrenal incidentalomas in the EURINE-ACT study: a prospective test validation study.

BACKGROUND: Cross-sectional imaging regularly results in incidental discovery of adrenal tumours, requiring exclusion of adrenocortical carcinoma (ACC). However, differentiation is hampered by poor specificity of imaging characteristics. We aimed to validate a urine steroid metabolomics approach, using steroid profiling as the diagnostic basis for ACC. METHODS: We did a prospective multicentre study in adult participants (age ≥18 years) with newly diagnosed adrenal masses. We assessed the accuracy of diagnostic imaging strategies based on maximum tumour diameter (≥4 cm vs <4 cm), imaging characteristics (positive vs negative), and urine steroid metabolomics (low, medium, or high risk of ACC), separately and in combination, using a reference standard of histopathology and follow-up investigations. With respect to imaging characteristics, we also assessed the diagnostic utility of increasing the unenhanced CT tumour attenuation threshold from the recommended 10 Hounsfield units (HU) to 20 HU. FINDINGS: Of 2169 participants recruited between Jan 17, 2011, and July 15, 2016, we included 2017 from 14 specialist centres in 11 countries in the final analysis. 98 (4·9%) had histopathologically or clinically and biochemically confirmed ACC. Tumours with diameters of 4 cm or larger were identified in 488 participants (24·2%), including 96 of the 98 with ACC (positive predictive value [PPV] 19·7%, 95% CI 16·2-23·5). For imaging characteristics, increasing the unenhanced CT tumour attenuation threshold to 20 HU from the recommended 10 HU increased specificity for ACC (80·0% [95% CI 77·9-82·0] vs 64·0% [61·4-66.4]) while maintaining sensitivity (99·0% [94·4-100·0] vs 100·0% [96·3-100·0]; PPV 19·7%, 16·3-23·5). A urine steroid metabolomics result indicating high risk of ACC had a PPV of 34·6% (95% CI 28·6-41·0). When the three tests were combined, in the order of tumour diameter, positive imaging characteristics, and urine steroid metabolomics, 106 (5·3%) participants had the result maximum tumour diameter of 4 cm or larger, positive imaging characteristics (with the 20 HU cutoff), and urine steroid metabolomics indicating high risk of ACC, for which the PPV was 76·4% (95% CI 67·2-84·1). 70 (3·5%) were classified as being at moderate risk of ACC and 1841 (91·3%) at low risk (negative predictive value 99·7%, 99·4-100·0). INTERPRETATION: An unenhanced CT tumour attenuation cutoff of 20 HU should replace that of 10 HU for exclusion of ACC. A triple test strategy of tumour diameter, imaging characteristics, and urine steroid metabolomics improves detection of ACC, which could shorten time to surgery for patients with ACC and help to avoid unnecessary surgery in patients with benign tumours. FUNDING: European Commission, UK Medical Research Council, Wellcome Trust, and UK National Institute for Health Research, US National Institutes of Health, the Claire Khan Trust Fund at University Hospitals Birmingham Charities, and the Mayo Clinic Foundation for Medical Education and Research.

The Mayo Clinic Histiocytosis Working Group Consensus Statement for the Diagnosis and Evaluation of Adult Patients With Histiocytic Neoplasms: Erdheim-Chester Disease, Langerhans Cell Histiocytosis, and Rosai-Dorfman Disease.

Histiocytic neoplasms, a rare and heterogeneous group of disorders, primarily include Erdheim-Chester disease, Langerhans cell histiocytosis, and Rosai-Dorfman disease. Due to their diverse clinical manifestations, the greatest challenge posed by these neoplasms is the establishment of a diagnosis, which often leads to a delay in institution of appropriate therapy. Recent insights into their genomic architecture demonstrating mitogen-activated protein kinase/extracellular signal-regulated kinase pathway mutations have now enabled potential treatment with targeted therapies in most patients. This consensus statement represents a joint document from a multidisciplinary group of physicians at Mayo Clinic who specialize in the management of adult histiocytic neoplasms. It consists of evidence- and consensus-based recommendations on when to suspect these neoplasms and what tests to order for the diagnosis and initial evaluation. In addition, it also describes the histopathologic and individual organ manifestations of these neoplasms to help the clinicians in identifying their key features. With uniform guidelines that aid in identifying these neoplasms, we hope to improve the awareness that may lead to their timely and correct diagnosis.