Immunologic Profiling of Immune-Related Cutaneous Adverse Events with Checkpoint Inhibitors Reveals Polarized Actionable Pathways.

PURPOSE: Immune-related cutaneous adverse events (ircAEs) occur in ≥50% of patients treated with checkpoint inhibitors (CPI), but mechanisms are poorly understood. EXPERIMENTAL DESIGN: Phenotyping/biomarker analyses were conducted in 200 patients on CPIs (139 with ircAEs, 61 without, control) to characterize their clinical presentation and immunologic endotypes. Cytokines were evaluated in skin biopsies, skin tape strip (STS) extracts and plasma using real-time PCR and Meso Scale Discovery multiplex cytokine assays. RESULTS: Eight ircAE phenotypes were identified: pruritus (26%), maculopapular rash (MPR; 21%), eczema (19%), lichenoid (11%), urticaria (8%), psoriasiform (6%), vitiligo (5%), and bullous dermatitis (4%). All phenotypes showed skin lymphocyte and eosinophil infiltrates. Skin biopsy PCR revealed the highest increase in IFN-gamma mRNA in patients with lichenoid (p<0.0001) and psoriasiform dermatitis (p<0.01) as compared to patients without ircAEs, while the highest IL-13 mRNA levels were detected in the eczema (p<0.0001, compared to control). IL-17A mRNA was selectively increased in psoriasiform (p<0.001), lichenoid (p<0.0001), bullous dermatitis (p<0.05) and MPR (p<0.001), compared to control. Distinct cytokine profiles were confirmed in STS and plasma. Analysis determined increased skin/plasma IL-4 cytokine in pruritus, skin IL-13 in eczema, plasma IL-5 and IL-31 in eczema and urticaria, and mixed-cytokine pathways in MPR. Broad inhibition via corticosteroids or type 2-cytokine targeted inhibition resulted in clinical benefit in these ircAEs. In contrast, significant skin upregulation of type 1/type 17 pathways was found in psoriasiform, lichenoid, bullous dermatitis, and type 1 activation in vitiligo. CONCLUSIONS: Distinct immunologic ircAE endotypes suggest actionable targets for precision medicine-based interventions.

Pruritus related to trastuzumab and pertuzumab in HER2 + breast cancer patients.

PURPOSE: The combination of trastuzumab and pertuzumab (HP) as part of a taxane-based regimen has shown benefit in the adjuvant and metastatic HER2 + breast cancer setting. In the CLEOPATRA trial, pruritus was reported in 11-17.6% of patients. The clinical phenotype and potential treatment strategies for this event have not been reported. METHODS: A retrospective review of 2583 patients receiving trastuzumab and pertuzumab for the treatment of HER2 + breast cancer from 11/23/2011 to 6/21/2021 was performed at Memorial Sloan Kettering Cancer Center (MSKCC). Patient demographics, pruritus characteristics, and treatments as documented in the electronic medical record (EMR) were included in this analysis. RESULTS: Of 2583 pts treated with HP, 122 (4.72%) with pruritus were identified. On average, patients experienced pruritus 319.0 days (8-3171) after initiation of HP. The upper extremities (67.4%), back (29.3%), lower extremities (17.4%), and shoulders (14.1%) were the most commonly affected regions. Grade 1/2 pruritus (97.6%) occurred in most cases. Patients responded primarily to treatment with topical steroids (52.2%), antihistamines (29.9%), emollients (20.9%), and gabapentinoids (16.4%). Of those with pruritus, 4 patients (3.3%) required treatment interruption or discontinuation. CONCLUSIONS: Pruritus is uncommon in patients on trastuzumab and pertuzumab, generally a chronic condition, with gabapentinoids or antihistamines representing effective therapies.

Clinical Utility of Melanoma Sentinel Lymph Node Biopsy Nomograms.

BACKGROUND: For patients with melanoma, the decision to perform sentinel lymph node biopsy (SLNB) is based on the estimated risk of lymph node metastasis. We assessed 3 melanoma SLNB risk-prediction models' statistical performance and their ability to improve clinical decision making (clinical utility) on a cohort of melanoma SLNB cases. STUDY DESIGN: Melanoma patients undergoing SLNB at a single center from 2003 to 2021 were identified. The predicted probabilities of sentinel lymph node positivity using the Melanoma Institute of Australia, Memorial Sloan Kettering Cancer Center (MSK), and Friedman nomograms were calculated. Receiver operating characteristic and calibration curves were generated. Clinical utility was assessed via decision curve analysis, calculating the net SLNBs that could have been avoided had a given model guided selection at different risk thresholds. RESULTS: Of 2,464 melanoma cases that underwent SLNB, 567 (23.0%) had a positive sentinel lymph node. The areas under the receiver operating characteristic curves for the Melanoma Institute of Australia, MSK, and Friedman models were 0.726 (95% CI, 0.702 to 0.750), 0.720 (95% CI, 0.697 to 0.744), and 0.721 (95% CI, 0.699 to 0.744), respectively. For all models, calibration was best at predicted positivity rates below 30%. The MSK model underpredicted risk. At a 10% risk threshold, only the Friedman model would correctly avoid a net of 6.2 SLNBs per 100 patients. The other models did not reduce net avoidable SLNBs at risk thresholds of ≤10%. CONCLUSIONS: The tested nomograms had comparable performance in our cohort. The only model that achieved clinical utility at risk thresholds of ≤10% was the Friedman model.

IL12/23 Blockade with Ustekinumab as a Treatment for Immune-Related Cutaneous Adverse Events.

Background: Immune-related cutaneous adverse events (ircAEs) are frequent and may reduce quality of life and consistent dosing. IL12/23 has been implicated in psoriasis, which is reminiscent of the psoriasiform/lichenoid ircAE phenotype. We report the use of ustekinumab as a therapeutic option. Methods: Patients at Memorial Sloan Kettering Cancer Center, New York, who received immune checkpoint inhibitors and were treated with ustekinumab or had the keywords "ustekinumab" or "Stelara" in their clinical notes between 1 March 2017 and 1 December 2022 were retrospectively identified via a database query. Documentation from initial and follow-up visits was manually reviewed, and response to ustekinumab was categorized into complete cutaneous response (CcR, decrease to CTCAE grade 0), partial cutaneous response (PcR, any decrease in CTCAE grade exclusive of decrease to grade 0), and no cutaneous response (NcR, no change in CTCAE grade or worsening). Labs including complete blood count (CBC), cytokine panels, and IgE were obtained in a subset of patients as standard of care. Skin biopsies were reviewed by a dermatopathologist. Results: Fourteen patients with psoriasiform (85.7%), maculopapular (7.1%), and pyoderma gangrenosum (7.1%) ircAEs were identified. Ten (71.4%) receiving ustekinumab had a positive response to treatment. Among these 10 responders, 4 (40%) demonstrated partial cutaneous response and 6 (60%) demonstrated complete cutaneous resolution. Six patients (42.9%) experienced interruptions to their checkpoint inhibitor treatment as a result of intolerable ircAEs, and following ircAE management with ustekinumab, two (33.3%) were successfully rechallenged with their checkpoint inhibitors. On histopathology, patients primarily had findings of interface or psoriasiform dermatitis. No patients reported an adverse event related to ustekinumab. Conclusions: Ustekinumab showed a benefit in a subset of patients with psoriasiform/lichenoid ircAEs. No safety signals were identified. However, further prospective randomized controlled trials are needed to confirm our findings.

Acute febrile neutrophilic dermatosis (Sweet syndrome) in acute myeloid leukemia patients: a 28-year institutional experience.

INTRODUCTION: Sweet syndrome (SS) is well-known to be associated with underlying hematologic malignancies. The incidence and qualities of SS among novel targeted therapies for acute myeloid leukemia (AML) have not yet been described. METHODS: Through retrospective review of 19432 patients diagnosed with acute/chronic leukemia or myelodysplastic syndromes/ myeloproliferative neoplasms (MDS+/-MPN) over 28 years, we calculated the incidence of SS in the setting of select hematologic malignancies and described the clinicopathologic characteristics of SS in patients with onset of SS after initiation of novel AML-targeted therapies. RESULTS: Overall incidence of SS was 0.36% (95% CI: 0.27% - 0.45%), which was significantly higher among patients with AML (50/5248, 0.94%; 95% CI: 0.71% - 1.25%). Nine AML patients were on 4 classes of novel targeted treatments - IDH1/2 inhibitor alone, FLT3 inhibitor, IDH2 and DOT1L inhibitor, and anti-CD33 therapy. In therapies inducing myeloid blast differentiation, SS occurred at later onset following treatment. CONCLUSIONS: In AML patients with fever and unusual skin lesions, physicians may consider SS earlier which may shorten time to diagnosis. Future assessments of SS among patients treated with novel therapies for AML and molecular studies of biopsies may help further explain this dermatologic adverse event with earlier diagnosis and management of neutrophilic dermatoses in these patients.

Management of immune-related cutaneous adverse events with dupilumab.

Immune checkpoint inhibitors (ICI) target the PD-1/PD-L1 and CTLA-4 pathways and allows the immune system to deliver antitumor effects. However, it is also associated with well-documented immune-related cutaneous adverse events (ircAEs), affecting up to 70-90% of patients on ICI. In this study, we describe the characteristics of and patient outcomes with ICI-associated steroid-refractory or steroid-dependent ircAEs treated with dupilumab. Patients with ircAEs treated with dupilumab between March 28, 2017, and October 1, 2021, at Memorial Sloan Kettering Cancer Center were included in this retrospective study, which assessed the rate of clinical response of the ircAE to dupilumab and any associated adverse events (AEs). Laboratory values were compared before and after dupilumab. All available biopsies of the ircAEs were reviewed by a dermatopathologist. Thirty-four of 39 patients (87%, 95% CI: 73% to 96%) responded to dupilumab. Among these 34 responders, 15 (44.1%) were complete responders with total ircAE resolution and 19 (55.9%) were partial responders with significant clinical improvement or reduction in severity. Only 1 patient (2.6%) discontinued therapy due to AEs, specifically, injection site reaction. Average eosinophil counts decreased by 0.2 K/mcL (p=0.0086). Relative eosinophils decreased by a mean of 2.6% (p=0.0152). Total serum immunoglobulin E levels decreased by an average of 372.1 kU/L (p=0.0728). The most common primary inflammatory patterns identified on histopathological examination were spongiotic dermatitis (n=13, 33.3%) and interface dermatitis (n=5, 12.8%). Dupilumab is a promising option for steroid-refractory or steroid-dependent immune-related cutaneous adverse events, particularly those that are eczematous, maculopapular, or pruritic. Among this cohort, dupilumab was well-tolerated with a high overall response rate. Nonetheless, prospective, randomized, controlled trials are warranted to confirm these observations and confirm its long-term safety.

Aggressive Cutaneous Lymphomas and Their Mimics.

Cutaneous lymphomas encompass a heterogeneous group of neoplasms with a wide spectrum of clinical presentations, histopathologic features, and prognosis. Because there are overlapping pathologic features among indolent and aggressive forms and with systemic lymphomas that involve the skin, clinicopathologic correlation is essential. Herein, the clinical and histopathologic features of aggressive cutaneous B- and T-cell lymphomas are reviewed. Indolent cutaneous lymphomas/lymphoproliferative disorders, systemic lymphomas, and reactive processes that may mimic these entities are also discussed. This article highlights distinctive clinical and histopathologic features, increases awareness of rare entities, and presents new and evolving developments in the field.

Case report: Later onset of NRAS-mutant metastatic melanoma in a patient with a partially-excised giant congenital melanocytic nevus.

Despite recent advances in treatment and surveillance, metastatic melanoma still carries a poor prognosis. Large/giant congenital melanocytic nevi (CMNs) constitute a known risk factor for the condition, with the greatest risk for malignant transformation thought to be during childhood (median age at diagnosis of 3 years in a previous cohort). Herein, we present the case of a 30-year-old male who, after undergoing multiple excision/grafting procedures for a giant CMN as a child, was diagnosed with an NRAS-mutant, MDM2-amplified metastatic melanoma more than 20 years later. Response to ipilimumab/nivolumab immunotherapy, cisplatin/vinblastine/temozolomide chemotherapy, and nivolumab/relatlimab immunotherapy was poor. This case highlights the importance of lifetime monitoring with once-yearly dermatological examination (including lymph node palpation) in large/giant CMN patients, as well as the need for further clinical trials evaluating novel therapies for NRAS-mutant melanoma.

Contribution of the Skin-Gut Axis to Immune-Related Adverse Events with Multi-System Involvement.

Immune-related adverse events (irAEs) frequently complicate treatment with immune checkpoint blockade (ICB) targeting CTLA-4, PD-1, and PD-L1, which are commonly used to treat solid and hematologic malignancies. The skin and gastrointestinal (GI) tract are most frequently affected by irAEs. While extensive efforts to further characterize organ-specific adverse events have contributed to the understanding and management of individual toxicities, investigations into the relationship between multi-organ toxicities have been limited. Therefore, we aimed to conduct a characterization of irAEs occurring in both the skin and gut. A retrospective analysis of two cohorts of patients treated with ICB at Memorial Sloan Kettering Cancer Center was conducted, including a cohort of patients with cutaneous irAEs (ircAEs) confirmed by dermatologists (n = 152) and a cohort of patients with biopsy-proven immune-related colitis (n = 246). Among both cohorts, 15% (61/398) of patients developed both skin and GI irAEs, of which 72% (44/61) patients had ircAEs preceding GI irAEs (p = 0.00013). Our study suggests that in the subset of patients who develop both ircAEs and GI irAEs, ircAEs are likely to occur first. Further prospective studies with larger sample sizes are needed to validate our findings, to assess the overall incidence of co-incident irAEs, and to determine whether ircAEs are predictors of other irAEs. This analysis highlights the development of multi-system dermatologic and gastrointestinal irAEs and underscores the importance of oncologists, gastroenterologists, and dermatologists confronted with an ircAE to remain alert for additional irAEs.

Association of HPV42 with digital papillary adenocarcinoma and the use of in situ hybridization for its distinction from acral hidradenoma and diagnosis at non-acral sites.

Digital papillary adenocarcinoma (DPAC) is a rare tumor of sweat gland origin that preferentially affects the digits and has the potential to metastasize. Its tumor diagnosis can be difficult. Well-differentiated variants of DPAC can be confused with a benign sweat gland tumor, in particular nodular hidradenoma. With the recent detection of HPV42 DNA in DPAC by next-generation sequence analysis, we reasoned that this association could be used for diagnostic purposes. To this end, we performed in situ hybridization for HPV42 on 10 tumors diagnosed as DPAC as well as 30 sweat gland tumors of various histology types, including 8 acral hidradenomas. All DPAC were positive for HPV42. Positive hybridization signals for HPV42 were seen in both primary and metastatic DPACs. All other tumors and normal tissues were negative. This study confirms the association of HPV42 with the tumor cells of DPAC through in situ hybridization. The positive test result in all lesions of DPAC and lack of detection of HPV42 in any of the acral hidradenomas or other sweat gland tumors examined in this series is encouraging for the potential diagnostic utility of the assay. As documented by two scrotal tumors of DPAC, the in situ hybridization test for HPV42 can also help support the rare occurrence of this tumor at a non-acral site.

Genomic landscape of cutaneous follicular lymphomas reveals 2 subgroups with clinically predictive molecular features.

Primary cutaneous follicle center lymphomas (PCFCLs) are indolent B-cell lymphomas that predominantly remain skin restricted and manageable with skin-directed therapy. Conversely, secondary cutaneous involvement by usual systemic follicular lymphoma (secondary cutaneous follicular lymphoma [SCFL]) has a worse prognosis and often necessitates systemic therapy. Unfortunately, no histopathologic or genetic features reliably differentiate PCFCL from SCFL at diagnosis. Imaging may miss low-burden internal disease in some cases of SCFLs, leading to misclassification as PCFCL. Whereas usual systemic FL is well characterized genetically, the genomic landscapes of PCFCL and SCFL are unknown. Herein, we analyzed clinicopathologic and immunophenotypic data from 30 cases of PCFCL and 10 of SCFL and performed whole-exome sequencing on 18 specimens of PCFCL and 6 of SCFL. During a median follow-up of 7 years, 26 (87%) of the PCFCLs remained skin restricted. In the remaining 4 cases, systemic disease developed within 3 years of diagnosis. Although the SCFLs universally expressed BCL2 and had BCL2 rearrangements, 73% of the PCFCLs lacked BCL2 expression, and only 8% of skin-restricted PCFCLs had BCL2 rearrangements. SCFLs showed low proliferation fractions, whereas 75% of PCFCLs had proliferation fractions >30%. Of the SCFLs, 67% had characteristic loss-of-function CREBBP or KMT2D mutations vs none in skin-restricted PCFCL. Both SCFL and skin-restricted PCFCL showed frequent TNFRSF14 loss-of-function mutations and copy number loss at chromosome 1p36. These data together establish PCFCL as a unique entity with biological features distinct from usual systemic FL and SCFL. We propose 3 criteria based on BCL2 rearrangement, chromatin-modifying gene mutations (CREBBP, KMT2D, EZH2, and EP300), and proliferation index to classify cutaneous FL specimens based on the likelihood of concurrent or future systemic spread.

Expanding the Spectrum of Microscopic and Cytogenetic Findings Associated With Spitz Tumors With 11p Gains.

A subset of Spitz tumors is associated with a copy number increase of chromosome 11p and activating mutations of HRAS. These aberrations have been reported to occur in association with desmoplastic Spitz nevi. Little is known to what extent 11p gains can also be found in nondesmoplastic tumors. To learn more about the spectrum of microscopic and cytogenetic changes that can be seen in Spitz lesions in association with 11p gains, we reviewed the clinical and pathologic features of 40 cases. Patient ages ranged from 3 to 75 years. The most common anatomic site was the head and neck region, followed by the upper extremities. Prominent desmoplasia was present in 10 cases. Seven tumors lacked significant stromal fibrosis. Twenty tumors were mitotically active. Novel microscopic features encountered in a few cases include a tumor with a polypoid silhouette and papillomatous surface and rare atypical tumors with a deep bulbous growth pattern. Among 36 cases analyzed by single-nucleotide polymorphism array or comparative genomic hybridization, 28 tumors had gains of the entire or near-entire p-arm of chromosome 11 with no other coexisting unbalanced genomic aberration. Eight cases had additional changes; 6 of these with 1 additional aberration per case, and 2 cases had several chromosomal aberrations. We also examined a subset of tumors by fluorescence in situ hybridization for the HRAS gene locus (11p15.5). All tumors were fluorescence in situ hybridization-positive. In conclusion, we expand the spectrum of pathologic findings associated with Spitz tumors with 11p gains. This cytogenetic aberration is not restricted to desmoplastic Spitz nevi. It can also be seen in nondesmoplastic and papillomatous lesions and atypical melanocytic tumors with a deep bulbous growth. We also document that in some Spitz tumors additional cytogenetic aberrations may be found, the significance of which remains to be determined.

Immune checkpoint inhibitor-related dermatologic adverse events.

Immune checkpoint inhibitors have emerged as a pillar in the management of advanced malignancies. However, nonspecific immune activation may lead to immune-related adverse events, wherein the skin and its appendages are the most frequent targets. Cutaneous immune-related adverse events include a diverse group of inflammatory reactions, with maculopapular rash, pruritus, psoriasiform and lichenoid eruptions being the most prevalent subtypes. Cutaneous immune-related adverse events occur early, with maculopapular rash presenting within the first 6 weeks after the initial immune checkpoint inhibitor dose. Management involves the use of topical corticosteroids for mild to moderate (grades 1-2) rash, addition of systemic corticosteroids for severe (grade 3) rash, and discontinuation of immunotherapy with grade 4 rash. Bullous pemphigoid eruptions, vitiligo-like skin hypopigmentation/depigmentation, and psoriasiform rash are more often attributed to programmed cell death-1/programmed cell death ligand-1 inhibitors. The treatment of bullous pemphigoid eruptions is similar to the treatment of maculopapular rash and lichenoid eruptions, with the addition of rituximab in grade 3-4 rash. Skin hypopigmentation/depigmentation does not require specific dermatologic treatment aside from photoprotective measures. In addition to topical corticosteroids, psoriasiform rash may be managed with vitamin D3 analogues, narrowband ultraviolet B light phototherapy, retinoids, or immunomodulatory biologic agents. Stevens-Johnson syndrome and other severe cutaneous immune-related adverse events, although rare, have also been associated with checkpoint blockade and require inpatient care as well as urgent dermatology consultation.

Immunohistochemistry for PRAME in the Distinction of Nodal Nevi From Metastatic Melanoma.

The distinction of metastatic melanoma from melanocytic nevi in lymph nodes can on occasion be difficult. As diffuse immunohistochemical (IHC) PRAME (PReferentially expressed Antigen in MElanoma) expression is detected in the majority of primary and metastatic melanomas, but rarely in nevi, we reasoned that PRAME could be a useful adjunct marker for the diagnosis of melanocytes in lymph nodes. In this study, we examined 45 nodal melanocytic deposits comprising 30 nodal nevi and 15 melanoma metastases. The latter were diagnostically not straightforward because they either coexisted with nodal nevi or were present in perinodal fibrous tissue. All nodal nevi (30/30) were negative for PRAME, whereas all melanoma metastases (15/15) were diffusely positive for PRAME IHC. We additionally report the novel use of a PRAME/Melan A dual-label immunostain. Our results show that PRAME IHC may be useful in the assessment of diagnostically challenging nodal melanocytic deposits, such as intraparenchymal nodal nevi, metastases confined to the capsular fibrous tissue, or in the setting of small metastases coexisting with a nodal nevus in the same lymph node.

Angiotropism in primary cutaneous melanoma is associated with disease progression and distant metastases: A retrospective study of 179 cases.

BACKGROUND: Angiotropism is the histopathological correlate of pericytic mimicry and extravascular migratory metastasis (EVMM), a mechanism of melanoma spread by migration along the external surface of blood and lymphatic vessels. The frequency of angiotropism in primary cutaneous melanoma and the clinical utility of its detection remain unclear. METHODS: We investigated angiotropism in 179 primary cutaneous melanomas by hematoxylin and eosin (H&E), CD31, and S100/D240 stains. RESULTS: We detected angiotropism in 31 cases (17%) by H&E. CD31 immunohistochemistry increased detection to 59 cases (33%). When lymphatic vessels were included by using S100/D240 stains, 67 cases (37%) cases were positive. Angiotropism was associated with lymphatic invasion and mitotic rate with all detection methods. There was an association with increased tumor thickness when detected by H&E and CD31. No association with sentinel lymph node status was seen. By H&E and CD31 staining, angiotropism was associated with disease progression and distant metastases by univariate, but not multivariate analysis. Overall survival was not affected by the presence of angiotropism. CONCLUSIONS: Angiotropism is relatively common in primary melanoma when immunohistochemical stains are used for detection and associated with mitotic rate and intravascular lymphatic invasion. The association with disease progression and distant metastasis suggests that it represents an alternative pathway of metastasis, that is, EVMM/pericytic mimicry vs intravascular spread.

Factors associated with false-negative pathologic diagnosis of calciphylaxis.

BACKGROUND: Calciphylaxis is a rare, painful, and debilitating disorder of vascular calcification and skin necrosis that typically affects patients with advanced kidney disease. During our routine pathology practice, we noted several missed diagnoses on calciphylaxis consultation cases originating from outside institutions and sought to explore factors associated with false-negative pathologic diagnosis of calciphylaxis. METHODS: The pathology database of a large tertiary academic medical center was retrospectively searched for "calciphylaxis" in inside reports on outside surgical consultation cases between 2007 and 2017. Inside and outside pathology reports were compared and medical records were searched for calciphylaxis clinical diagnosis and risk factors. RESULTS: Twenty-four calciphylaxis patients were identified, with median age of 63.5 years. Seven of 24 (29%) of specimens were inadequate (e.g., lack of subcutaneous adipose tissue for evaluation). Eight of 17 (47%) of adequate specimens had a first false-negative pathologic diagnosis of calciphylaxis. Histochemical staining for calcium significantly correlated with true-positive diagnosis (93% vs 55%, P = 0.004). Dermatopathology fellowship training significantly correlated with true-positive diagnosis (82% vs 38%, P = 0.047). CONCLUSIONS: Adequate sampling, dermatopathology training, and use of histochemical stains to identify calcium associate with decreased false-negative rate for calciphylaxis diagnosis. These findings need further evaluation in larger prospective studies.

Genomic Analyses Identify Recurrent Alterations in Immune Evasion Genes in Diffuse Large B-Cell Lymphoma, Leg Type.

Cutaneous diffuse large B-cell lymphomas (DLBCLs) are aggressive lymphomas with a poor prognosis. To elucidate their genetic bases, we analyzed exome sequencing of 37 cutaneous DLBCLs, including 31 DLBCLs, leg type (DLBCL-LT) and 6 cutaneous DLBCLs-not otherwise specified (DLBCL-NOS). As reported previously, 77% of DLBCL-LT harbor NF-κB-activating MYD88 mutations. In nearly all MYD88-wild-type DLBCL-LT, we found cancer-promoting mutations that either activate the NF-κB pathway through alternative genes (NFKBIE or REL) or activate other canonical cancer pathways (BRAF, MED12, PIK3R1, and STAT3). After NF-κB, the second most commonly mutated pathway putatively enables immune evasion via mutations predicted to downregulate antigen processing (B2M, CIITA, HLA) or T-cell co-stimulation (CD58). DLBCL-LT have little genetic overlap with the genetically heterogeneous DLBCL-NOS. Instead, they resemble primary central nervous system and testicular large B-cell lymphomas (primary central nervous system lymphomas and primary testicular lymphomas). Like primary central nervous system lymphomas/primary testicular lymphomas, 40% of DLBCL-LT (vs. 0% of DLBCLs-not otherwise specified) harbored PDL1/PDL2 translocations, which lead to overexpression of PD-L1 or PD-L2 in 50% of the cases. Collectively, these data broaden our understanding of cutaneous DLBCLs and suggest novel therapeutic approaches (e.g., BRAF or PI3K inhibitors). Additionally, they suggest novel treatment paradigms, wherein DLBCL-LT can be targeted with strategies (e.g., immune checkpoint blockers) currently being developed for genomically similar primary central nervous system lymphomas/primary testicular lymphomas.