The immune response to a Coxiella burnetii vaccine in sheep varies according to their natural pre-exposure.

Q fever in humans is caused by Coxiella (C.) burnetii. In 2008 and 2012, cases of Q fever in humans were linked to an infected flock of approximately 650 ewes. Since 2013 gimmers (G'13, G'14, G'15 etc.) were primary vaccinated (two doses) with an inactivated C.burnetii vaccine without any revaccination. In 2013, 30 ewes were primary vaccinated (A'13). Shedding was annually monitored by qPCR-testing of vaginal and nasal swabs collected at lambing. Animals were tested for Phase I- (PhI) and PhII-antibodies (Ab) and for PhII-specific-interferon-γ (IFN-γ) before and after vaccination. The effect of a revaccination was determined in 2018 and 2023. Groups of randomly selected gimmers primary vaccinated in 2015, 2016 and 2017 and a mixed group of older animals (A'13, G'13 and G'14) were revaccinated once in 2018. The trial was repeated in 2023 on groups primary vaccinated in 2019-2023. Major shedding after the outbreak in 2012 ceased in 2014. Thereafter C.burnetii was only sporadically detected at low-level in 2018, 2021 and 2023. Sheep naturally exposed to C.burnetii during the outbreak in 2012 (A'13, G'13) mounted a strong and complete (PhI, PhII, IFN-γ) recall immune response after vaccination. A serological PhI+/PhII+ pattern dominated after vaccination. In contrast, since 2014 a weaker immune response (PhII-titre, IFN-γ) and a dominance of the PhI-/PhII+ pattern was observed in vaccinated gimmers. The number of serologically non-responding gimmers to vaccination increased to 25.0 % in G'16/G'17 and 40.4 % in G'19/G'20. But revaccination even three (G'15 in 2018) and four (G'19 in 2023) years after primary vaccination resulted in a strong and complete immune response. No difference of the immune response nor to more recently primary vaccinated animals (G'23 in 2023) nor to those animals that were present during the outbreak (A'13/G'13/G'14 in 2018) was observed.

CXCR4-Directed Imaging and Endoradiotherapy in Desmoplastic Small Round Cell Tumors.

Desmoplastic small round cell tumor (DSRCT) is a rare, radiosensitive, yet difficult-to-treat sarcoma subtype affecting predominantly male adolescents. Extensive intraperitoneal seeding is common and requires multimodal management. With no standard therapy established, the prognosis remains poor, and new treatment options are needed. We demonstrate the clinical potential of C-X-C motif chemokine receptor 4 (CXCR4)-directed imaging and endoradiotherapy in DSRCT. Methods: Eight male patients underwent dual-tracer imaging with [18F]FDG and CXCR4-directed [68Ga]pentixafor PET/CT. A visual comparison of both tracers, along with uptake quantification in active DSRCT lesions, was performed. [68Ga]pentixafor uptake was correlated with immunohistochemical CXCR4 expression on tumor cells. Four patients with end-stage progressive disease underwent CXCR4-based endoradiotherapy. We report the safety, response by RECIST 1.1, and survival after endoradiotherapy. Results: Uptake of [68Ga]pentixafor in tumor lesions was demonstrated in all patients with DSRCT, providing diagnostic power comparable to [18F]FDG PET. Corresponding CXCR4 expression was confirmed by immunohistochemistry in all DSRCT biopsies. Finally, 4 patients were treated with CXCR4-directed [90Y]endoradiotherapy, 3 in a myeloablative dose range with subsequent autologous stem cell transplantation. All 3 required transfusions, and febrile neutropenia occurred in 2 patients (resulting in 1 death). Notably, severe nonhematologic adverse events were absent. We observed signs of response in all 3 patients, translating into disease stabilization in 2 patients for 143 and 176 d, respectively. In the third patient, postmortem autopsy confirmed a partial pathologic response. Conclusion: We validated CXCR4 as a diagnostic biomarker and a promising target for endoradiotherapy in DSRCT, demonstrated its feasibility, and provided the first evidence of its clinical efficacy.

Twenty-four months of bacterial colonialization and infection rates in patients with transcutaneous osseointegrated prosthetic systems after lower limb amputation-A prospective analysis.

Background: Transcutaneous osseointegrated prosthesis systems (TOPS) are alternative rehabilitation methods to socket prosthetics, after limb amputation. TOPS compromise a two-step surgery: starting with the implantation of the stem which is then followed by the creation of the transcutaneous stoma through which the exoprosthesis can be connected. Immediately after surgery, this opening is permanently exposed to pathogens. This study aimed to investigate the dynamics of bacterial colonization of the stoma to analyze whether obligate bacterial colonization leads to a risk of periprosthetic infections after TOPS treatment. Methods: This prospective study analyzed data from 66 patients (aged 26-75 years) after TOPS treatment between 2017 and 2019. Microbiological swabs from the stoma were analyzed on the first postoperative day and 3, 6, 12, and 24 months after stoma creation. Infection rates, laboratory values (CRP, leukocyte count, hemoglobin), and body temperature were recorded at these points in time. Statistical analysis was performed using SPSS 28. Results: The results show the formation of a stable environment dominated by Gram-positive bacteria in the stoma of TOPS patients over 24 months. Staphylococcus aureus, Staphylococcus spp., and Streptococcus spp. were the most common species found. With regard to the cohort up to the 3 months follow-up, 7.9% (five patients) developed infections surrounding the TOPS procedure. In relation to the whole cohort with loss to follow-up of 80.3% at the 24 months follow-up the infection rates increased up to 38.3%. Conclusion: The soft tissue inside and around the transcutaneous stoma is colonialized by multiple taxa and changes over time. A stable Gram-positive dominated bacterial taxa could be a protective factor for ascending periprosthetic infections and could possibly explain the relatively low infection rate in this study as well as in literature.

Panel Sequencing of Primary Cutaneous B-Cell Lymphoma.

BACKGROUND: Primary cutaneous follicular B-cell lymphoma (PCFBCL) represents an indolent subtype of Non-Hodgkin's lymphomas, being clinically characterized by slowly growing tumors of the skin and common cutaneous relapses, while only exhibiting a low propensity for systemic dissemination or fatal outcome. Up to now, only few studies have investigated underlying molecular alterations of PCFBCL with respect to somatic mutations. OBJECTIVES: Our aim was to gain deeper insight into the pathogenesis of PCFBCL and to delineate discriminatory molecular features of this lymphoma subtype. METHODS: We performed hybridization-based panel sequencing of 40 lymphoma-associated genes of 10 cases of well-characterized PCFBCL. In addition, we included two further ambiguous cases of atypical B-cell-rich lymphoid infiltrate/B-cell lymphoma of the skin for which definite subtype attribution had not been possible by routine investigations. RESULTS: In 10 out of 12 analyzed cases, we identified genetic alterations within 15 of the selected 40 target genes. The most frequently detected alterations in PCFBCL affected the TNFRSF14, CREBBP, STAT6 and TP53 genes. Our analysis unrevealed novel mutations of the BCL2 gene in PCFBCL. All patients exhibited an indolent clinical course. Both the included arbitrary cases of atypical B-cell-rich cutaneous infiltrates showed somatic mutations within the FAS gene. As these mutations have previously been designated as subtype-specific recurrent alterations in primary cutaneous marginal zone lymphoma (PCMZL), we finally favored the diagnosis of PCMZL in these two cases based on these molecular findings. CONCLUSIONS: To conclude, our molecular data support that PCFBCL shows distinct somatic mutations which may aid to differentiate PCFBCL from pseudo-lymphoma as well as from other indolent and aggressive cutaneous B-cell lymphomas. While the detected genetic alterations of PCFBCL did not turn out to harbor any prognostic value in our cohort, our molecular data may add adjunctive discriminatory features for diagnostic purposes on a molecular level.

Long-term control of Coxiellosis in sheep by annual primary vaccination of gimmers.

Coxiella (C.) burnetii, a Gram-negative intracellular bacterium, causes Q fever in humans and Coxiellosis in animals. Ruminants are a primary source of human infection with C.burnetii. In 2013, vaccination was implemented in a sheep flock with 650 ewes associated with two outbreaks of Q fever in humans in 2008 and 2012. Only gimmers (yearlings) received two doses of a commercial C.burnetii phase I whole cell vaccine three weeks apart (primary vaccination) without any revaccination. Vaginal and nasal swabs collected shortly after lambing were tested by qPCR. Additionally, a group of non-vaccinated sentinels was serologically monitored for phase I (PhI), II (PhII) antibodies and for Interferon γ (IFN-γ) after stimulation of whole blood cells with PhII-antigen with and without an IL-10-neutralizing monoclonal antibody. In 2021, 679 sera collected in 2014-2021 were retested retrospectively with three commercial ELISA kits and one batch of an in-house PhI/PhII-ELISA. A low-level shedding of C.burnetii (<103 mean C.burnetii/swab) was observed until 2014. In 2021 C.burnetii was detected in two animals (<103.1C.burnetii/swab), but vaginal swabs collected at two subsequent lambing seasons remained negative. Seroconversion of sentinels was detected until 2017. However, the retrospective analysis of sentinels in 2021 revealed additional single seropositive animals from 2018 to 2021. IFN-γ reactivity was observed during the whole study period; it peaked in 2014 and in 2018 and decreased thereafter. The sporadic detection of C.burnetii and the immune responses of sentinels suggested that a subliminal infection persisted despite vaccination. Nevertheless, vaccination of gimmers prevented the development of a major outbreak, it controlled the infection and reduced the risk of human infection.

Autophagy Blockage Reduces the Incidence of Pancreatic Ductal Adenocarcinoma in the Context of Mutant Trp53.

Macroautophagy (hereafter referred to as autophagy) is a homeostatic process that preserves cellular integrity. In mice, autophagy regulates pancreatic ductal adenocarcinoma (PDAC) development in a manner dependent on the status of the tumor suppressor gene Trp53. Studies published so far have investigated the impact of autophagy blockage in tumors arising from Trp53-hemizygous or -homozygous tissue. In contrast, in human PDACs the tumor suppressor gene TP53 is mutated rather than allelically lost, and TP53 mutants retain pathobiological functions that differ from complete allelic loss. In order to better represent the patient situation, we have investigated PDAC development in a well-characterized genetically engineered mouse model (GEMM) of PDAC with mutant Trp53 (Trp53 R172H ) and deletion of the essential autophagy gene Atg7. Autophagy blockage reduced PDAC incidence but had no impact on survival time in the subset of animals that formed a tumor. In the absence of Atg7, non-tumor-bearing mice reached a similar age as animals with malignant disease. However, the architecture of autophagy-deficient, tumor-free pancreata was effaced, normal acinar tissue was largely replaced with low-grade pancreatic intraepithelial neoplasias (PanINs) and insulin expressing islet ß-cells were reduced. Our data add further complexity to the interplay between Atg7 inhibition and Trp53 status in tumorigenesis.

Recurrent Alterations in the MAPK pathway in Sporadic Pyogenic Granuloma of Childhood.

Pyogenic granuloma is one of the most common vascular tumours. The cause of pyogenic granuloma was previously thought to be an inflammatory reaction with consecutive stimulation of endothelial cell proliferation. However, recent studies suggest that pyogenic granuloma may be driven by constitutive activation of the mitogen-activated protein kinase pathway. The aim of this study was to investigate the molecular profile of sporadic pyogenic granuloma of childhood, using a systematic approach scrutinizing potential aberrations within different oncogenic pathways. Within a retrospective setting pyogenic granuloma of 15 patients was analysed by targeted next generation sequencing using the Oncomine Focus Assay, which includes genes of key tumorigenic signalling pathways. Activating mutations were found in 4 out of 15 cases (27%). Two HRAS hotspot mutations (p.Gly13Arg, p.Ala59Thr), 1 BRAF (p.Val600Glu) mutation and a novel, previously not reported, MAP2K1 hotspot mutation (p.Glu203Lys) were identified. It is notable that all of these genes are involved in constitutive mitogen- activated protein kinase signalling. This study increases the range of underlying genetic alterations in pyogenic granuloma by identifying novel oncogenic mutations in crucial mitogen-activated protein kinase pathway genes. The results provide supporting evidence that activated mitogen-activated protein kinase signalling is a key driver in the pathogenesis of pyogenic granuloma, which might be exploited by targeted treatment approaches for selected cases.

Acute systemic knockdown of Atg7 is lethal and causes pancreatic destruction in shRNA transgenic mice.

The notion that macroautophagy/autophagy is a potentially attractive therapeutic target for a variety of diseases, including cancer, largely stems from pre-clinical mouse studies. Most of these examine the effects of irreversible and organ confined autophagy deletion using site specific Cre-loxP recombination of the essential autophagy regulating genes Atg7 or Atg5. Model systems with the ability to impair autophagy systemically and reversibly at all disease stages would allow a more realistic approach to evaluate the consequences of authophagy inhibition as a therapeutic concept and its potential side effects. Here, we present shRNA transgenic mice that via doxycycline (DOX) regulable expression of a highly efficient miR30-E-based shRNA enabled knockdown of Atg7 simultaneously in the majority of organs, with the brain and spleen being noteable exceptions. Induced animals deteriorated rapidly and experienced profound destruction of the exocrine pancreas, severe hypoglycemia and depletion of hepatic glycogen storages. Cessation of DOX application restored apparent health, glucose homeostasis and pancreatic integrity. In a similar Atg5 knockdown model we neither observed loss of pancreatic integrity nor diminished survival after DOX treatment, but identified histological changes consistent with steatohepatitis and hepatic fibrosis in the recovery period after termination of DOX. Regulable Atg7-shRNA mice are valuable tools that will enable further studies on the role of autophagy impairment at various disease stages and thereby help to evaluate the consequences of acute autophagy inhibition as a therapeutic concept.Abbreviations: ACTB: actin, beta; AMY: amylase complex; ATG4B: autophagy related 4B, cysteine peptidase; ATG5: autophagy related 5; ATG7: autophagy related 7; Cag: CMV early enhancer/chicken ACTB promoter; Col1a1: collagen, type I, alpha 1; Cre: cre recombinase; DOX: doxycycline; GCG: glucagon; GFP: green fluorescent protein; INS: insulin; LC3: microtubule-associated protein 1 light chain 3; miR30-E: optimized microRNA backbone; NAFLD: non-alcoholic fatty liver disease; NASH: non-alcoholic steatohepatitis; PNLIP: pancreatic lipase; rtTA: reverse tetracycline transactivator protein; SQSTM1/p62: sequestome 1; TRE: tetracycline responsive element.

Oncogenic Mutations and Gene Fusions in CD30-Positive Lymphoproliferations and Clonally Related Mycosis Fungoides Occurring in the Same Patients.

The emergence of a common progenitor cell has been postulated for the association of CD30-positive lymphoproliferative disease (LPD) and mycosis fungoides (MF) within the same patient. Up to now, no comprehensive analysis has yet addressed the genetic profiles of such concurrent lymphoma subtypes. We aimed to delineate the molecular alterations of clonally related CD30-positive LPD and MF occurring in the same two patients. We analyzed the molecular profile of 16 samples of two patients suffering both from CD30-positive LPD and MF being obtained over a time course of at least 5 years. To detect oncogenic mutations, we applied targeted sequencing technologies with a hybrid capture-based DNA library preparation approach, and for the identification of fusion transcripts, an anchored multiplex PCR enrichment kit was used. In all samples of CD30-positive LPD and MF, oncogenic fusions afflicting the Jak/signal transducer and activator of transcription signaling pathway were present, namely NPM1‒TYK2 in patient 1 and ILF3‒JAK2 in patient 2. Additional signal transducer and activator of transcription 5A gene STAT5A mutations exclusively occurred in lesions of CD30-positive LPD in one patient. CD30-positive LPD and MF may share genetic events when occurring within the same patients. Constitutive activation of the Jak/signal transducer and activator of transcription signaling pathway may play a central role in the molecular pathogenesis of both entities.

Targeted Deep Sequencing of Mycosis Fungoides Reveals Intracellular Signaling Pathways Associated with Aggressiveness and Large Cell Transformation.

INTRODUCTION: Large-cell transformation (LCT) of mycosis fungoides (MF) has been associated with a higher risk of relapse and progression and, consequently, restricted prognosis. Its molecular pathogenesis has not been elucidated yet. MATERIALS AND METHODS: In order to address molecular mechanisms of LCT, we performed hybrid capture panel-based sequencing of skin biopsies from 10 patients suffering from MF with LCT versus 17 patients without LCT including follow-up biopsies during clinical course, respectively (51 samples in total). The analyzed patients were attributed to three different groups based on the presence of LCT and clinical behavior. RESULTS: While indolent MF cases without LCT did not show pathogenic driver mutations, a high rate of oncogenic alterations was detected in patients with LCT and aggressive clinical courses. Various genes of different oncogenic signaling pathways, including the MAPK and JAK-STAT signaling pathways, as well as epigenetic modifiers were affected. A high inter-individual and distinctive intra-individual mutation diversity was observed. Oncogenic RAS mutations were exclusively detected in patients with LCT. CONCLUSION: Our data demonstrate that LCT transition of MF is associated with increased frequency of somatic mutations in cancer-associated genes. In particular, the activation of RAS signaling-together with epigenetic dysregulation-may crucially contribute to the molecular pathogenesis of the LCT phenotype, thus conveying its adverse clinical behavior.

The histological and molecular spectrum of lipoblastoma: A case series with identification of three novel gene fusions by targeted RNA-sequencing.

Lipoblastoma is a rare benign mesenchymal neoplasm that typically occurs in infancy but may also occur in older age groups and various locations. Thus, there are often numerous clinical differential diagnoses. Moreover, lipoblastomas can show a broad histologic spectrum, which can hamper the correct diagnosis, particularly in small biopsies. At the genomic level, lipoblastomas are characterized by chromosomal fusions involving the PLAG1 gene. We investigated 11 lipoblastoma samples from 10 pediatric patients (age range five months to 12 years), including one patient with local recurrence, in view of their histopathological features, and performed targeted RNA sequencing. We found a broad histological spectrum with some tumors with prominent myxoid changes, but also tumors composed mainly of mature adipocytic cells, and classified the cases according to the literature as classic (mixed), maturing, or myxoid subtype. By targeted RNA sequencing analysis, we identified characteristic PLAG1 rearrangements in 70% of the investigated cases. Moreover, these analyses revealed three novel gene fusions, two affecting the PLAG1 gene and one involving HMGA2. Besides, we performed PLAG1 immunohistochemistry and identified positive cells, typically immature adipocytic cells and spindle cells, at various numbers in all cases. However, in the maturing areas, only very sparsely positive cells were found, limiting the value of the PLAG1 immunohistochemistry as an adjunct in the diagnosis of lipoblastoma, particularly for the maturing subtype and small biopsies. The presented case series confirms the broad morphological spectrum of lipoblastoma described in the literature and underlines the value of modern molecular diagnostic approaches as a supportive diagnostic tool in challenging cases and for gaining further insights into the molecular basis of this rare mesenchymal tumor.

EBER in situ hybridization in subcutaneous aluminum granulomas/lymphoid hyperplasia: A diagnostic clue to differentiate injection-associated lymphoid hyperplasia from other forms of pseudolymphomas and cutaneous lymphomas.

BACKGROUND: Subcutaneous vaccination or desensitization may induce persistent nodules at the injection sites. Without the knowledge of prior injection, histopathological work-up may be challenging. OBJECTIVE: Aim of this study was to contribute to the histopathological work-up of unclear subcutaneous nodules, especially their differentiation from cutaneous lymphoma. METHODS: We retrospectively reviewed clinical data and histopathological slides of four patients with subcutaneous nodules, which were suspected to suffer from cutaneous T- or B-cell lymphoma. Sections of these cases and 12 negative controls were stained with hematoxylin and eosin and a standardized immunohistochemical panel of B- and T-cell markers including EBER in situ hybridization as well as electron microscopy. RESULTS: In all cases, large histiocytes with granular cytoplasm compatible with intracellular aluminum hydroxide were present. EBER in situ hybridization revealed positive staining of these granular histiocytes while staining was absent in negative controls. LIMITATIONS: Post hoc completion of medical history revealed that vaccination or specific immunotherapy had been applied before at the biopsy site in only three out of four patients; one patient was lost to follow-up. CONCLUSION: EBER in situ hybridization is an adjunctive tool to differentiate aluminum-induced granuloma/lymphoid hyperplasia from other forms of pseudolymphoma and cutaneous B- or T-cell lymphomas.

The transcription factor NRF2 enhances melanoma malignancy by blocking differentiation and inducing COX2 expression.

The transcription factor NRF2 is the major mediator of oxidative stress responses and is closely connected to therapy resistance in tumors harboring activating mutations in the NRF2 pathway. In melanoma, such mutations are rare, and it is unclear to what extent melanomas rely on NRF2. Here we show that NRF2 suppresses the activity of the melanocyte lineage marker MITF in melanoma, thereby reducing the expression of pigmentation markers. Intriguingly, we furthermore identified NRF2 as key regulator of immune-modulating genes, linking oxidative stress with the induction of cyclooxygenase 2 (COX2) in an ATF4-dependent manner. COX2 is critical for the secretion of prostaglandin E2 and was strongly induced by H2O2 or TNFα only in presence of NRF2. Induction of MITF and depletion of COX2 and PGE2 were also observed in NRF2-deleted melanoma cells in vivo. Furthermore, genes corresponding to the innate immune response such as RSAD2 and IFIH1 were strongly elevated in absence of NRF2 and coincided with immune evasion parameters in human melanoma datasets. Even in vitro, NRF2 activation or prostaglandin E2 supplementation blunted the induction of the innate immune response in melanoma cells. Transcriptome analyses from lung adenocarcinomas indicate that the observed link between NRF2 and the innate immune response is not restricted to melanoma.

Recurrent Oncogenic JAK and STAT Alterations in Cutaneous CD30-Positive Lymphoproliferative Disorders.

The group of cutaneous CD30-positive lymphoproliferative disorders (LPD) comprises two different entities, namely lymphomatoid papulosis (LyP) and cutaneous anaplastic large T-cell lymphoma (cALCL). LyP constitutes a benign lymphoproliferation with spontaneously regressing papules, whereas cALCL presents with solitary or multiple skin tumors with a low propensity to disseminate. To elucidate the hitherto largely unknown molecular pathogenesis of these entities, we performed comprehensive next-generation sequencing in a well-characterized cohort of 12 patients. Considering the low tumor cell content of LyP, we applied targeted sequencing technologies with a hybrid capture-based DNA library preparation approach and for the identification of fusion transcripts an anchored multiplex PCR enrichment kit. As the major finding, we detected, in 50% of LPD, genetic events that implied a constitutively activated Janus kinase-signal transducer and activator of transcription signaling (JAK-STAT) pathway in these entities. The identified molecular aberrations comprised either pathogenic STAT mutations or oncogenic fusion transcripts comprising effector domains of JAK. With respect to LyP, we report to our knowledge such previously unreported genetic aberrations in this specific entity. The detection of these convergent aberrations within the JAK-STAT signaling pathway deciphers common potential driving mechanisms of lymphomagenesis within LPD being shared between LyP and cALCL. Moreover, the presence of these oncogenic alterations paves the way to develop novel personalized treatment strategies.

Paraproteinaemia in Primary Cutaneous Marginal Zone Lymphoma.

Primary cutaneous marginal zone lymphomas (PCMZL) frequently exhibit lymphoplasmacytoid/plasmacytic differentiation, implying the capacity to produce monoclonal immunoglobulins. As these paraproteins are secreted, and thus are measurable in blood and urine, they may correlate with disease burden and serve as tumour markers reflecting therapeutic response. This study retrospectively analysed the records of 23 patients with PCMZL. During treatment and follow-up, laboratory tests, including full blood count, lactate dehydrogenase, serum protein electrophoresis and turbidimetric analyses, were conducted. Thirty-nine percent of cases showed a suspicious serum protein electrophoresis in terms of paraproteinaemia. In 44% of cases the heavy and light chain restriction in tissue samples correlated with serological findings. Altogether, 89% of the PCMZL patients with paraproteinaemia eventually experienced a relapse, in contrast to 62% of the group without paraproteinaemia. This study analysed the incidence and clinical implications of paraproteinaemia in patients with PCMZL. A clear correlation was found between paraproteinaemia, tumour relapse and therapeutic intervention.

Panel Sequencing Shows Recurrent Genetic FAS Alterations in Primary Cutaneous Marginal Zone Lymphoma.

Primary cutaneous marginal zone lymphoma (PCMZL) represents an indolent subtype of non-Hodgkin lymphoma that is clinically characterized by slowly growing skin tumors with a very low propensity for systemic dissemination. The underlying genetic basis of PCMZL has not been comprehensively elucidated. To gain deeper insight into the molecular pathogenesis of PCMZL, we performed hybridization-based panel sequencing of 38 patients with well-characterized PCMZL. In 32 of the 38 patients, we identified genetic alterations within 39 selected target genes. The most frequently detected alterations (24/38 patients, 63.2%) affected the FAS gene, of which 22 patients harbored alterations, which affect the functionally relevant death domain of the apoptosis-regulating FAS/CD95 protein in a dominant-negative manner. In addition, we identified highly recurrent mutations in three other genes, namely SLAMF1, SPEN, and NCOR2. Our molecular data suggest that apoptosis defects provide the molecular basis of the observed clinical features of PCMZL, which commonly presents with only slowly growing skin tumors, reflecting its invariably indolent behavior. From a diagnostic point of view, highly recurrent FAS mutations in PCMZL presumably separate this indolent lymphoma entity from pseudolymphoma, and this adds adjunctive discriminatory features at a molecular level.