Consensus on performing skin biopsies, laboratory workup, evaluation of tissue samples and reporting of the results in patients with suspected cutaneous graft-versus-host disease

Chronic graft-versus-host disease. Part I: Epidemiology, pathogenesis, and clinical manifestations

Chronic graft-versus-host disease is a major complication of allogeneic hematopoietic cell transplantation and a leading cause of long-term morbidity, nonrelapse mortality, and impaired health-related quality of life. The skin is commonly affected and presents heterogeneously, making the role of dermatologists critical in both diagnosis and treatment. In addition, new clinical classification and grading schemes inform treatment algorithms, which now include 3 U.S. Food and Drug Administration-approved therapies, and evolving transplant techniques are changing disease epidemiology. Part I reviews the epidemiology, pathogenesis, clinical manifestations, and diagnosis of chronic graft-versus-host disease. Part II discusses disease grading and therapeutic management.

Understanding and treatment of cutaneous graft-versus-host-disease

The skin is the outermost mechanical barrier where dynamic immune reactions take place and is the most commonly affected site in both acute and chronic graft-versus-host disease (GVHD). If not properly treated, pain and pruritis resulting from cutaneous GVHD can increase the risk of secondary infection due to erosions, ulcerations, and damage of underlying tissues. Furthermore, resulting disfiguration can cause distress and significantly impact patients' quality of life. Thus, a deeper understanding of skin-specific findings of GVHD is needed. This review will highlight some promising results of recent pre-clinical studies on the pathophysiology of skin GVHD and summarize the diagnostic and staging/grading procedures according to the clinical manifestations of skin GVHD. In addition, we will summarize outcomes of various GVHD treatments, including skin-specific response rates.

Dermatologic complications in transplantation and cellular therapy for acute leukemia

Adoptive cellular immunotherapy, mainly hematopoietic stem cell transplant and CAR-T cell therapy have revolutionized treatment of patients with acute leukemia. Indications and inclusion criteria for these treatments have expanded in recent years. While these therapies are associated with significant improvements in disease response and overall survival, patients may experience adverse events from associated chemotherapy conditioning, engraftment, cytokine storm, supportive medications, and post-transplant maintenance targeted therapies. Supportive oncodermatology is a growing specialty to manage cutaneous toxicities resulting from the anti-cancer therapies. In this review, we summarize diagnosis and management of the common cutaneous adverse events including drug eruptions, graft-versus-host disease, neoplastic and paraneoplastic complications in patients undergoing cellular therapies.

The Relevance of Skin Biopsies in General Internal Medicine: Facts and Myths

Introduction

Non-dermatology medical specialties may refer patients for skin biopsies, searching for a particular diagnosis. However, the diagnostic impact of the skin biopsy is not clearly established. This article aims to assess the indications for, and evaluate the clinical relevance of, skin biopsies in non-dermatology medical specialties.

Methods

A questionnaire was sent to 23 non-dermatology specialty departments in a university medical center, requesting a list of indications for skin biopsies, as well as to 10 staff dermatologists to collect the indications of skin biopsies requested by non-dermatology specialties. Once the indications were collected, a literature search was performed to evaluate their clinical value and relevance.

Results

Eleven non-dermatology specialties provided a list of skin biopsy indications, to which staff dermatologists added seven more indications. A literature search revealed evidence-based medicine data for six diseases, that is, amyloidosis, peripheral autonomic neuropathy, Sneddon’s syndrome, intravascular lymphoma, sarcoidosis, and chronic graft-versus-host disease. Results were questionable concerning infectious endocarditis, acute graft-versus-host-disease, and the lupus band test. Skin biopsy were not evidenced as useful for the diagnosis of calciphylaxis, systemic scleroderma, Behçet’s disease, or hypermobile Ehlers–Danlos syndrome. For the diagnosis of Alport’s syndrome, pseudoxanthoma elasticum, and vascular Ehlers–Danlos syndrome, skin biopsy is currently outperformed by genetic analyses. For diagnoses such as Henoch–Schönlein purpura and Sjögren’s syndrome, skin biopsy represents an additional item among other diagnostic criteria.

Conclusion

The usefulness of skin biopsy as requested by non-dermatology specialties is only evidenced for amyloidosis, peripheral autonomic neuropathy, Sneddon’s syndrome, intravascular lymphoma, sarcoidosis, chronic graft-versus-host-disease, Henoch–Schönlein purpura, and Sjögren’s syndrome.

Real-Time Reflectance Confocal Microscopy of Cutaneous Graft-versus-Host Disease Correlates with Histopathology

Reflectance confocal microscopy (RCM) allows noninvasive, real-time evaluation of the skin at a resolution akin to histopathology (HP), but its application in cutaneous graft-versus-host disease (GVHD) has not been extensively assessed. We describe RCM features of cutaneous GVHD including acute (aGVHD), late acute, chronic (cGVHD; sclerotic and nonsclerotic subtypes), and inactive GVHD and correlate RCM with same-site HP for a subset of patients. Thirty-two adult and pediatric allogeneic hematopoietic cell transplantation (allo-HCT) recipients with cutaneous GVHD received RCM imaging of ≥1 lesions (n = 44), 13 of which necessitated skin biopsy. RCM images were deidentified and assessed by 2 RCM experts blinded to clinical and HP findings to reach a consensus on the features and patterns of the inflammatory dermatoses. Major RCM features (present in ≥65% of lesional sites) and patterns were reported. To determine the correlation between RCM and HP, detection of cellular features and patterns of inflammatory dermatoses were compared using percent agreement and prevalence-adjusted, bias-adjusted kappa estimates. Seven patients with early or late aGVHD (7 lesions) had irregular honeycombing, spongiosis, dermoepidermal junction (DEJ) and dermal inflammation, and melanophages; those with early aGVHD also had hyperkeratosis, dilated vessels, and coarse connective tissue. Both groups had an interface dermatitis pattern. Eighteen patients with nonsclerotic cGVHD (24 lesions) had irregular honeycombing, spongiosis, DEJ and dermal inflammation, dilated vessels, coarse connective tissue, and interface and spongiotic dermatitis patterns. Three sclerotic patients with cGVHD (7 lesions) had irregular honeycombing, DEJ and dermal inflammation with an interface dermatitis pattern. Four patients with inactive GVHD (6 lesions) showed minimal inflammation. RCM and HP had similar detection rates for 6 of 13 features and overall patterns important for diagnosis in 2 patients with late aGVHD (2 lesions; 15%) and 10 with nonsclerotic cGVHD (11 lesions; 85%) necessitating skin biopsy. RCM can detect features commonly reported in cutaneous GVHD and is comparable to HP. Additional characterization of cutaneous GVHD by RCM may enable future use in diagnosing, monitoring, or predicting disease in real time.

Steroid-refractory chronic graft-versus-host disease: treatment options and patient management

Chronic graft-versus-host disease (cGVHD) is one of the major causes of late mortality after allogenic hematopoietic stem cell transplantation. Moderate-to-severe cGVHD is associated with poor health-related quality of life and substantial disease burden. While corticosteroids with or without calcineurin inhibitors comprise the first-line treatment option, the prognosis for patients with steroid-refractory cGVHD (SR-cGVHD) remains poor. The mechanisms underlying steroid resistance are unclear, and there are no standard second-line treatment guidelines for patients with SR-cGVHD. In this review, we provide an overview on current treatment options of cGVHD and use a series of theoretical case studies to elucidate the rationale of choices of second- and third-line treatment options for patients with SR-cGVHD based on individual patient profiles.

Inpatient Management of Mucocutaneous GVHD

Purpose of Review

Graft-versus-host disease (GVHD) is an immune mediated disorder affecting 30 - 70% of patients after allogeneic hematopoietic stem cell transplantation (alloHSCT), and is a major cause of morbidity and non-relapse mortality (NRM) [1]. Dermatologists play a critical role in acute and chronic GVHD, as skin involvement is common and often the earliest involved site of disease [2].

Recent Findings

GVHD shares clinical and histopathological features with a variety of other skin diseases, requiring thorough consideration of differential diagnoses in hematopoietic stem cell transplantation (HSCT) recipients with lesions suggestive of cutaneous GVHD. Treatment considerations for GVHD are influenced by factors such as disease classification, overall grading, organ involvement, associated symptoms, and immunological anti-tumor effect. Several treatments are available and may be indicated as monotherapy or adjuvant therapy to allow faster withdrawal or tapering of immunosuppression. While corticosteroids are often first line therapy, oral ruxolitinib has been recently approved for treatment of steroid-refractory aGHVD, and oral ibrutinib has been approved for steroid-refractory cGHVD.

Summary

This article provides current clinical, diagnostic, and therapeutic considerations relevant to the hospitalist for both acute and chronic mucocutaneous GVHD. Optimal inpatient management of these diseases requires an interdisciplinary team.

Cutaneous manifestations of acute and chronic graft-versus-host disease

Graft-versus-host disease (GvHD) is a commonly occurring immunological reaction and frequent complication following allogeneic hematopoietic stem cell transplantation. Its highly diverse manifestations including skin involvement as the most common appearance of GvHD, can dramatically influence patient's quality of life, in particular in the chronic stage, in addition to patient's decreased survival outcome. Hence, the role of the dermatologist has become very crucial in an interdisciplinary setting, particularly since appearances of GvHD in the skin can be multifaceted and challenging. Clinical manifestation of the acute GvHD (aGvHD) is limited to erythematous maculopapular rash and oral mucosal lesions while the chronic form manifests in a wider range in a localized area or disseminated including involvement of nail, scalp and genital area. This article aims to provide a comprehensive overview on the variable cutaneous presentations of acute and chronic GvHD for a proper and early diagnosis on the one hand, and to discuss updated therapeutic options for both acute and chronic GvHD on the other hand, to initiate an adequate treatment to obtain the most beneficial clinical outcome.

A clinical and histological comparison between acute cutaneous graft-versus-host disease and other maculopapular eruptions following hematopoietic stem cell transplantation: a retrospective cohort

BACKGROUND

Prompt management of acute graft-versus-host disease (GVHD) may prevent its morbidity and mortality. Maculopapular (MP) eruption is a presenting sign of acute GVHD, but differentiation from other causes of MP rash is challenging.

METHODS

A retrospective study was conducted among patients developing MP eruptions after allogeneic hematopoietic stem cell transplantation. We compared the clinical and histopathological differences between an acute cutaneous GVHD (group 1) and other MP eruptions (group 2). We also determined the clinical prognostic indicators linked to acute GVHD severity, morbidity, and mortality.

RESULTS

Of 95 patients identified, 75 met the classification criteria for acute GVHD, and 25 had other MP eruptions. Palm and/or sole involvement was more frequently found (51.4% vs. 12%, odds ratio [OR] [95% confidence interval] = 7 [2.1, 23.7], P < 0.01 and 41.4% vs. 0%, OR 37.2 [2.2, 635], P < 0.01, respectively) in group 1 than in group 2. Comparing the histological features between the two groups, necrotic keratinocytes in basal and spinous layers (92.9% vs. 22.2%, OR 27 [3.5, 594.7], P < 0.01) and (85.7% vs. 33.3%, OR 9.3 [1.4, 60.8], P = 0.02, respectively), diffuse basal vacuolization (42.9% vs. 0%, OR 14.5 [0.7, 298.2], P = 0.04), lymphocyte satellitosis (71.4% vs. 0%, OR 44.3 [2.1, 936.8], P < 0.01), and subepidermal clefts (42.9% vs. 0%, OR 14.5 [0.7, 298.2], P = 0.04) were significantly more apparent in group 1. Among extracutaneous presentations, diarrhea alone and/or accompanied by hyperbilirubinemia (47.1% vs. 16%, OR 4.3 [1.4, 13.1], P = 0.03 and 27.1% vs. 0%, OR 19.3 [1.1, 332.8], P < 0.01, respectively) and newly developed transaminitis (37.1% vs. 12%, OR 3.3 [1.1, 12.6], P = 0.02) suggested the diagnosis of acute GVHD. Mucosal involvement and/or blister formation correlated with severe acute GVHD (OR 26.6 [5.4, 130.4], P < 0.01). Skin and systemic GVHD severity correlated with time to rash resolution (P = 0.03 and P = 0.04, respectively), length of hospital stays (P < 0.01 and P < 0.01, respectively), and mortality (OR 4.87 [1.4, 17.4], P = 0.02 and OR 4.6 [1.3, 16.5], P = 0.02, respectively).

CONCLUSIONS

Our findings may be beneficial tools for establishing the diagnosis of acute GVHD.

Eczematous graft-vs-host disease: A report of three cases and review of the literature

Graft-vs-host disease (GVHD) is the most common complication following hematopoietic cell transplantation, which affects skin frequently. Acute and chronic forms of GVHD manifest commonly as maculopapular to morbilliform eruptions and sclerotic or lichen-planus-like lesions, respectively; however, atypical presentations such as eczema-like GVHD may occur at times. We describe three cases of GVHD with diverse and polymorphous cutaneous eruptions including pompholyx-like and vasculitis-like rash as well as erythematous plaques and papulosquamous eruptions, with skin biopsy showing unifying histopathological findings with concurrent changes of spongiotic dermatitis and vacuolar interface reaction with apoptotic keratinocytes. In addition, the clinical and pathological features of previously reported cases of eczema-like GVHD are reviewed. It is emphasized that the course of the disease can be variable and successful management often involves a combination of multiple therapeutic modalities including immunosuppression with or without ultraviolet therapy. These cases highlight the importance of meticulous clinicopathological correlation with careful exclusion of mimicking conditions to arrive at the correct diagnosis.

Dermoscopy of Cutaneous Graft-Versus-Host-Disease in Patients After Allogeneic Hematopoietic Stem Cell Transplantation

Introduction

Progress in the transplant procedure has resulted in a higher proportion of patients with long-term survival after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Cutaneous graft-versus-host disease (GvHD) occurs often among patients who have undergone allo-HSCT. Routine diagnosis of skin and mucosal lesions is based primarily on clinical evaluation and histopathologic confirmation of skin biopsies. However, biopsy is an invasive method and histopathologic analysis is time-consuming, often accompanied by a lack of clinical correlation. There is therefore an urgent need for non-invasive, reproducible in vivo imaging methods that could be used in patients with cutaneous GvHD—both in the setting of initial diagnosis and during follow-up.The aim of the study reported here was to determine the role of dermoscopic monitoring of skin lesions in allo-HSCT recipients with consecutive histopathologic support as a non-invasive, alternative method to diagnose GvHD.

Methods

Twenty patients were examined by dermoscopy upon the manifestation of skin changes in the course of GvHD. Consecutive skin biopsies for histopathologic analysis were obtained from the suspected skin locations determined during dermoscopy.

Results

Graft-versus-host disease was confirmed by histopathology in 19 of the 20 allo-HSCT recipients. Four patients developed symptoms of acute cutaneous GvHD (grade 1, n = 2; grade 2, n = 1; grade 3, n = 1), and 15 patients developed chronic cutaneous GvHD. The most frequent dermoscopic signs (irrespective of whether GvHD was chronic or acute) were vessels and scaling (both n = 14, 73.7%). Hyperpigmentation and white patchy areas were present in eight patients (42.1%). Fair to moderate levels of agreement were found between presence of melanophages in the skin sample and dermoscopic granularity (Cohen’s Kappa [κ] = 0.39), scaling (κ = − 0.3) and vessels (κ = − 0.42). The finding of white patchy areas was inversely associated with lymphocytic infiltration (κ = − 0.55).

Conclusion

The results of this study suggest that dermoscopy may be a useful tool for diagnosing cutaneous GvHD in allo-HSCT recipients. Combining the clinical picture with dermoscopic features may bring us closer to a faster and easier diagnosis of GvHD.

Are apoptosis-determining techniques useful to establish an early diagnosis of acute graft-vs-host disease in pediatric patients under treatment with multiple drugs?

BACKGROUND

There are no pathognomonic histopathological features to distinguish acute graft-vs-host disease (aGVHD) from skin drug reactions (SDRs) in pediatric patients with multiple drug regimens that have received blood transfusions and/or transplants. We aimed to determine if the addition of apoptosis markers is helpful to distinguish aGVHD from SDRs in these patients.

METHODS

Skin biopsy specimens from patients with a clinical diagnosis of aGVHD or SDRs were evaluated for the presence of apoptotic bodies, satellitosis, interface damage, vasculitis, and inflammatory infiltrate on H&E stain. Information was completed with apoptotic markers (transferase-mediated dUTP nick end-labeling [TUNEL], bcl-2, and caspase-3).

RESULTS

The skin biopsy specimens of 32 patients with aGVHD and 11 with SDRs were included for study. Only the number of apoptotic keratinocytes per 10 high-power fields (hpf) showed a significant difference between both groups (P = 0.02); the presence of ≥4 apoptotic keratinocytes per 10 hpf was identified as the optimal cut-off point to discriminate aGVHD from SDRs. No SDRs cases had follicular apoptotic cells. TUNEL, bcl-2, and caspase-3 determination showed no difference between both groups.

CONCLUSIONS

The presence of ≥4 apoptotic keratinocytes per 10 hpf (in aGVHD) and the absence of follicular apoptotic cells (in SDRs) might be a useful marker to distinguish between them.

Common and critical inflammatory dermatoses every pathologist should know

Inflammatory dermatopathology remains a challenging area for surgical pathologists. Yet every surgical pathologist encounters inflammatory dermatoses as part of routine practice. This review will focus on selected diagnoses that are either commonly encountered in the routine practice of surgical pathology or are critically important. The following entities will be covered: spongiotic dermatoses, lichen simplex chronicus, and early lichen sclerosus in the setting of vulvar biopsies, as well as graft versus host disease, Stevens-Johnson syndrome/toxic epidermal necrolysis, granuloma anulare, pyoderma gangrenosum, and calciphylaxis. Practical points and key histologic features will be emphasized.

Cutaneous Graft-Versus-Host Disease: Diagnosis and Treatment

Graft-versus-host disease (GVHD) is an immunological reaction and a frequent complication following allogeneic hematopoietic stem cell transplantation. It is associated with high mortality rates and may have a significant negative impact on the patient's quality of life, particularly in the chronic-stage setting. Many different organs can be involved, which leads to a wide range of clinical manifestations. In this context, dermatologists play a key role by diagnosing and treating GVHD from the outset since cutaneous features are not just the most common but are also usually the presenting sign. Several skin-direct therapies are available and may be indicated as monotherapy or adjuvant treatment in order to allow faster tapering and withdrawal of systemic immunosuppression. Treatment of steroid-refractory patients remains a challenge and, to date, no consensus has been reached for one single agent in second-line therapy. This article aims to review skin involvement as well as provide and update discussion on therapeutic options for both acute and chronic cutaneous GVHD.

Optical coherence tomography angiography of normal skin and inflammatory dermatologic conditions

BACKGROUND

In clinical dermatology, the identification of subsurface vascular and structural features known to be associated with numerous cutaneous pathologies remains challenging without the use of invasive diagnostic tools.

OBJECTIVE

To present an advanced optical coherence tomography angiography (OCTA) method to directly visualize capillary-level vascular and structural features within skin in vivo.

METHODS

An advanced OCTA system with a 1310 nm wavelength was used to image the microvascular and structural features of various skin conditions. Subjects were enrolled and OCTA imaging was performed with a field of view of approximately 10 × 10 mm. Skin blood flow was identified using an optical microangiography (OMAG) algorithm. Depth-resolved microvascular networks and structural features were derived from segmented volume scans, representing tissue slabs of 0-132, 132-330, and 330-924 μm, measured from the surface of the skin.

RESULTS

Subjects with both healthy and pathological conditions, such as benign skin lesions, psoriasis, chronic graft-versus-host-disease (cGvHD), and scleroderma, were OCTA scanned. Our OCTA results detailed variations in vascularization and local anatomical characteristics, for example, depth-dependent vascular, and structural alterations in psoriatic skin, alongside their resolve over time; vascular density changes and distribution irregularities, together with corresponding structural depositions in the skin of cGvHD patients; and vascular abnormalities in the nail folds of a patient with scleroderma.

CONCLUSION

OCTA can image capillary blood flow and structural features within skin in vivo, which has the potential to provide new insights into the pathophysiology, as well as dynamic changes of skin diseases, valuable for diagnoses, and non-invasive monitoring of disease progression and treatment. Lasers Surg. Med. 50:183-193, 2018. © 2018 Wiley Periodicals, Inc.

Lichenoid and interface dermatoses

The terms 'lichenoid' and 'interface' dermatitis are often used interchangeably to describe an inflammatory pattern characterized histologically by damage to the basal keratinocytes in the epidermis. The mechanism of cell damage of such cells is now best understood as apoptosis, or programmed cell death. This inflammatory pattern of dermatoses, is also accompanied frequently by a band of lymphocytes and histiocytes in the superficial dermis, that often obscures the dermal-epidermal junction, hence the term 'lichenoid'. A discussion of the more common lichenoid/interface dermatitides encountered in the routine clinical practice encompasses the following entities: lichen planus, lupus erythematosus, dermatomyositis, erythema multiforme, graft versus host disease, fixed drug reactions, and multiple others.

High frequency of cutaneous manifestations including vitiligo and alopecia areata in a prospective cohort of patients with chronic graft-vs-host disease

Aim

To determine the frequency and the characteristics of cutaneous manifestations, especially vitiligo and alopecia areata, in patients with chronic graft-vs-host disease (cGVHD).

Methods

50 patients with cGVHD were prospectively enrolled in the observational study protocol and evaluated by an experienced dermatologist. The evaluation was focused on the clinical spectrum of skin and adnexal involvement, and the cutaneous GVHD score was determined according to National Institutes of Health (NIH) Consensus criteria. The presence of vitiligo, alopecia, xerosis, nail changes, and dyspigmentation was also assessed.

Results

Out of 50 cGVHD patients, 28 (56%) had skin involvement, and 27 of them (96%) had hypo and/or hyperpigmentations. 11 patients (39%) had a mild cutaneous NIH cGVHD score, 22% moderate, and 39% severe. 15 (30%) patients had nail changes and 10 (20%) had vitiligo or alopecia areata. Univariate analysis showed that patients with vitiligo/alopecia areata received more lines of prior systemic immunosuppressive therapy (P = 0.043), had lower Karnofsky performance status (P = 0.028), and had a higher B-cell number (P = 0.005), platelet count (P = 0.022), and total protein (P = 0.024). Vitiligo and alopecia areata were associated with higher NIH skin score (P = 0.001), higher intensity of immunosuppressive treatment (P = 0.020), and total body irradiation conditioning (P = 0.040). Multivariate regression model showed that patients with higher NIH skin scoring were 3.67 times more likely to have alopecia and/or vitiligo (odds ratio 3.67; 95% confidence interval 1.26-10.73), controlled for all other factors in the model (age at study entry, number of B-cells, platelet count, and global NIH score).

Conclusion

These data indicate that vitiligo and alopecia areata occur more frequently in cGVHD than previously reported.

Dermatologic emergencies in a tertiary hospital: A descriptive study

BACKGROUND AND OBJECTIVE

Dermatology in-house call is uncommon in the Spanish national health system. The objective of the present study was to define the groups of dermatologic diseases and conditions most frequently seen in the emergency department and to evaluate the need for dermatology in-house call in the training of medical residents.

MATERIAL AND METHODS

We performed a descriptive study of all patients who attended the emergency department with a skin complaint during a 1-year period (June 2013 to May 2014) and were assessed by 9 dermatology residents. The study variables were date/day, sex, age, diagnosis, special surgical procedures, additional laboratory tests, and need for hospitalization and/or follow-up. We also evaluated patients attending their first scheduled visit to the dermatologist between January and June 2014 in order to compare the most frequent conditions in both groups.

RESULTS

A total of 3084 patients attended the emergency room with a skin complaint (5.6% of all visits to the emergency department), and 152 different diagnoses were made. The most frequent groups of diseases were infectious diseases (23%) and eczema (15.1%). The specific conditions seen were acute urticaria (7.6%), contact dermatitis (6.1%), and drug-induced reactions (4.6%). By contrast, the most frequent conditions seen in the 1288 patients who attended a scheduled dermatology appointment were seborrheic keratosis (11.9%), melanocytic nevus (11.5%), and actinic keratosis (8%). A follow-up visit was required in 42% of patients seen in the emergency department. Fourth-year residents generated the lowest number of follow-up visits.

CONCLUSIONS

We found that infectious diseases and eczema accounted for almost 40% of all emergency dermatology visits. Our results seem to indicate that the system of in-house call for dermatology residents is very useful for the hospital system and an essential component of the dermatology resident's training program.

NIH Consensus development project on criteria for clinical trials in chronic graft-versus-host disease: II. The 2014 Pathology Working Group Report

The 2005 National Institute of Health (NIH) Consensus Conference outlined histopathological diagnostic criteria for the major organ systems affected by both acute and chronic graft-versus-host disease (GVHD). The 2014 Consensus Conference led to this updated document with new information from histopathological studies of GVHD in the gut, liver, skin, and oral mucosa and an expanded discussion of GVHD in the lungs and kidneys. The recommendations for final histological diagnostic categories have been simplified from 4 categories to 3: no GVHD, possible GVHD, and likely GVHD, based on better reproducibility achieved by combining the previous categories of "consistent with GVHD" and "definite GVHD" into the single category of "likely GVHD." Issues remain in the histopathological characterization of GVHD, particularly with respect to the threshold of histological changes required for diagnostic certainty. Guidance is provided for the incorporation of biopsy information into prospective clinical studies of GVHD, particularly with respect to biomarker validation.