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Objective: Digital pathology is an opportunity to revise the routine and old artisanal workflow, moving to standard operating procedures, quality control and reproducibility. Here the results of a survey promoted by the Coordinamento della Medicina di Laboratorio (CRC Med Lab) of the Lombardy region in Italy are reported to shed light on the current situation of digital adoption in the country. Methods: The survey composed of 58 questions was sent to 60 pathology laboratories. The results were collected and most significant answers were reported and discussed. Results: Answers were received from 57 (95%) laboratories, a minority organized in spoke-hub networks (16%) with a centralized processing phase (11%). Hybrid manual/computer-assisted traceability was prevalent (36%), with QR/barcode labeling starting within the pathology lab (23%). Different laboratory information systems (LIS) were employed, mostly with alert functions and/or multimedial file attachments (56% and 46%, respectively). The majority opted for a semi-automated tracking management (44, 77%) and 18 centers (32%) were partly digitizing the routine (¾ scanning < 25% of slides). Whole slide images were retained for 3.7 years in average; in-house blocks/slides archiving was still preferred (30, 53%), with 1838 (±1551) and 1798 (±1950) days (5 years) internal permanence for blocks and slides that are stored in out-source (mean turnaround time for return on-demand 3.7±2.1, range 1-10 days). Conclusions: The advantages of digital pathology must be balanced against the challenges faced in the structural revision of the pathology workflow. This regional scouting can represent the foundation to build an efficient and connected digital pathology system in the territory.
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Fluxo de Trabalho , Itália/epidemiologia , Humanos , Inquéritos e Questionários , Patologia Clínica , Sistemas de Informação em Laboratório Clínico , Laboratórios Clínicos , Reprodutibilidade dos Testes , Controle de QualidadeRESUMO
The 5th WHO classification of thoracic tumours includes thoracic SMARCA4-deficient undifferentiated tumour (SMARCA4-UT) among the "other epithelial tumours of the lung" chapter. Herein, we present a case of undifferentiated thoracic neoplasm with retention of SMARCA4 expression, lack of NUT fusion protein and loss of SMARCB1/INI1 expression. After presenting the clinical and pathological features of the tumour, we carried out a review of the literature on the same topic. Albeit very rare, we believe this entity should be included in the heterogeneous group of undifferentiated neoplasms of the thorax.
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DNA Helicases , Proteína SMARCB1 , Neoplasias Torácicas , Fatores de Transcrição , Humanos , Proteína SMARCB1/deficiência , Proteína SMARCB1/genética , Fatores de Transcrição/genética , Fatores de Transcrição/deficiência , Neoplasias Torácicas/patologia , Neoplasias Torácicas/genética , DNA Helicases/deficiência , DNA Helicases/genética , Proteínas Nucleares/genética , Proteínas Nucleares/deficiência , Masculino , Feminino , Biomarcadores Tumorais/análise , Biomarcadores Tumorais/genética , Pessoa de Meia-Idade , Neoplasias Pulmonares/patologia , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/diagnósticoRESUMO
A cutaneous carcinosarcoma (cCS) is a rare and aggressive skin cancer characterized by both carcinomatous (epithelial) and sarcomatous (mesenchymal) components, making it a biphasic tumor. Despite its occurrence in various organs, a cCS is exceptionally rare in the skin, predominantly affecting older males. The etiology of a cCS is unclear, but it may originate from a single progenitor cell capable of dual differentiation or from a collision of carcinoma and sarcoma cells. Clinically, a cCS presents as a rapidly growing, painful, ulcerated nodule or plaque on sun-exposed skin, with a high risk of local invasion and metastasis. Histopathologically, a cCS includes various epithelial components, such as squamous cell carcinoma and basal cell carcinoma, along with undifferentiated sarcomatous components resembling atypical fibroxanthoma. The tumor may also exhibit heterologous differentiation like angiosarcomatous or rhabdomyosarcomatous features. We present three cases of a cCS, highlighting their clinical and histological characteristics and comparing them with previously reported cases. Understanding a cCS is complicated by its rarity and diverse presentation, emphasizing the need for further research to elucidate its pathogenesis and optimal management.
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In the molecular era, proper archival conditions within pathology laboratories are crucial, especially for formalin-fixed paraffin-embedded (FFPE) tissue specimens retrieved years after the original diagnosis. Indeed, improper preservation can impact the integrity of nucleic acids and protein antigens. This study evaluates the quality status of stored FFPE blocks using multilevel omics approaches. FFPE blocks from 45 Non-Small Cell Lung Carcinoma (NSCLC) cases were analyzed. The blocks were collected from six different pathology archives across Italy with distinct environmental characteristics. Nucleic acids' quantity and quality, as well as protein antigens, were assessed using various techniques, including MALDI-MSI. RNA was quantitatively higher, but more fragmented, compared to DNA. DNA quantity and quality were suitable for molecular analyses in 94.4% and 62.3% of samples, respectively. RNA quantity was adequate across all samples, but it was optimal only in 22.3% of cases. DNA quality started to deteriorate after 6-8 years, whereas RNA quality diminished only after 10 years of storage. These data might suggest a particular DNA susceptibility to FFPE blocks conservation. Immunohistochemical intensity decreased significantly after 6-8 years of storage, and MALDI-MSI analysis revealed that younger tissue blocks contained more unique proteomic signals than the older ones. This study emphasizes the importance of proper FFPE archiving conditions for molecular analyses. Governance should prioritize attention to pathology archives to ensure quality preservation and optimize predictive testing. By elucidating the nuances of FFPE block storage, this research paves the way for enhanced molecular diagnostics and therapeutic insights regarding oncology and beyond.
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The WHO Classification of Tumors, Thoracic Tumors, 5th edition, has outlined the use of TTF-1 and ΔNP63/P40 to discriminate between adenocarcinoma and squamous cell carcinoma. In 2015, the first description of a rare non-small cell lung carcinoma featuring co-expression of glandular and squamous differentiation within most of the same individual tumor cells was reported on, with ultrastructural and molecular demonstration of such a biphenotypic differentiation. We herein describe an additional case of this rare tumor entity, which is confirmed to be an aggressive neoplasm despite potential targets of therapy.
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Adenocarcinoma , Carcinoma Pulmonar de Células não Pequenas , Neoplasias Pulmonares , Humanos , Neoplasias Pulmonares/diagnóstico , Neoplasias Pulmonares/patologia , Carcinoma Pulmonar de Células não Pequenas/diagnóstico , Carcinoma Pulmonar de Células não Pequenas/patologia , Adenocarcinoma/diagnóstico , Adenocarcinoma/patologia , Pulmão/patologia , Prognóstico , Biomarcadores TumoraisRESUMO
BACKGROUND: Methylthioadenosine phosphorylase (MTAP) is an essential metabolic enzyme in the purine and methionine salvage pathway. In cancer, MTAP gene copy number loss (MTAP loss) confers a selective dependency on the related protein arginine methyltransferase 5. The impact of MTAP alterations in gastrointestinal (GI) cancers remains unknown although hypothetically druggable. Here, we aim to investigate the prevalence, clinicopathological features and prognosis of MTAP loss GI cancers. METHODS: Cases with MTAP alterations were retrieved from The Cancer Genome Atlas (TCGA) and a real-world cohort of GI cancers profiled by next-generation sequencing. If MTAP alterations other than loss were found, immunohistochemistry was performed. Finally, we set a case-control study to assess MTAP loss prognostic impact. RESULTS: Findings across the TCGA dataset (N=1363 patients) and our cohort (N=508) were consistent. Gene loss was the most common MTAP alteration (9.4%), mostly co-occurring with CDKN2A/B loss (97.7%). Biliopancreatic and gastro-oesophageal cancers had the highest prevalence of MTAP loss (20.5% and 12.7%, respectively), being mostly microsatellite stable (99.2%). In colorectal cancer, MTAP loss was rare (1.1%), while most MTAP alterations were mutations (5/7, 71.4%); among the latter, only MTAP-CDKN2B truncation led to protein loss, thus potentially actionable. MTAP loss did not confer worse prognosis. CONCLUSIONS: MTAP alterations are found in 5%-10% of GI cancers, most frequently biliopancreatic and gastro-oesophageal. MTAP loss is the most common alteration, identified almost exclusively in MSS, CDKN2A/B loss, upper-GI cancers. Other MTAP alterations were found in colorectal cancer, but unlikely to cause protein loss and drug susceptibility.
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The bacterial genotoxin colibactin promotes colorectal cancer (CRC) tumorigenesis, but systematic assessment of its impact on DNA repair is lacking, and its effect on response to DNA-damaging chemotherapeutics is unknown. We find that CRC cell lines display differential response to colibactin on the basis of homologous recombination (HR) proficiency. Sensitivity to colibactin is induced by inhibition of ATM, which regulates DNA double-strand break repair, and blunted by HR reconstitution. Conversely, CRC cells chronically infected with colibactin develop a tolerant phenotype characterized by restored HR activity. Notably, sensitivity to colibactin correlates with response to irinotecan active metabolite SN38, in both cell lines and patient-derived organoids. Moreover, CRC cells that acquire colibactin tolerance develop cross-resistance to SN38, and a trend toward poorer response to irinotecan is observed in a retrospective cohort of CRCs harboring colibactin genomic island. Our results shed insight into colibactin activity and provide translational evidence on its chemoresistance-promoting role in CRC.
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Neoplasias Colorretais , Escherichia coli , Peptídeos , Policetídeos , Humanos , Irinotecano/farmacologia , Escherichia coli/genética , Escherichia coli/metabolismo , Estudos Retrospectivos , DNA/metabolismo , Neoplasias Colorretais/tratamento farmacológico , Neoplasias Colorretais/genética , Neoplasias Colorretais/microbiologiaRESUMO
BACKGROUND: Intraluminal non-occlusive thrombus (ILT) is a rare cause of ischemic stroke. Although in most cases ILT is associated with arterial wall disorders, it has also been documented in patients with thrombophilic conditions. CASE REPORT: We present a case of carotid ILT in a 38-year-old puerperal woman with pregnancy-induced hypercoagulability. Following in vitro fertilization pregnancy, she experienced acute left-sided weakness 9 days after delivery. CT angiography revealed an intraluminal filling defect in the right carotid bulb, suggestive of a thrombus, along with ipsilateral MCA sub-occlusion. Mechanical thrombectomy was performed, achieving complete vessel recanalization without any endovascular intervention on the carotid ILT. Comprehensive evaluation excluded any underlying carotid vessel wall disease (such as atherosclerosis, inflammatory diseases, arterial dissection, focal dysplasia), inherited or acquired thrombophilia, and the sole prothrombotic risk factor identified was the puerperium. Histological thrombus analysis showed fibrin/platelet-rich material with significant macrophage infiltration (consistent with an intermediate/organized thrombus, suggesting potential embolization from a pre-existing carotid ILT). Anti-thrombotic treatment (acetylsalicylic acid 100 mg and enoxaparin 6000 UI) resulted in complete thrombus resolution at follow-up. CONCLUSION: ILT should be considered a potential case of embolic stroke in pregnancy or puerperium. Vessel imaging is essential for diagnosis. Histological thrombus analysis can provide insights into the pathophysiological mechanisms of stroke.
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Acidente Vascular Cerebral , Trombose , Adulto , Feminino , Humanos , Gravidez , Artéria Carótida Interna/patologia , Angiografia por Tomografia Computadorizada , Período Pós-Parto , Acidente Vascular Cerebral/complicações , Acidente Vascular Cerebral/diagnóstico por imagem , Trombose/complicações , Resultado do Tratamento , TrombectomiaRESUMO
BACKGROUND: Endovascular thrombectomy (EVT) is a treatment option in patients with a cerebral venous thrombosis (CVT) who deteriorate despite anticoagulant treatment. Assessment of thrombus composition in CVT may provide insights into the pathophysiology of the disease and suggest new therapeutic strategies. CASE REPORT: A 47-year-old woman (smoking habit and estradiol/progesterone-releasing intra-uterine device) diagnosed with massive CVT underwent EVT (complete recanalization via aspiration catheter and stentriever) due to acute-onset left-sided weakness and dysarthria despite 72 h of full-dose subcutaneous low-molecular heparin. Two main reddish clots (maximum diameter 15 mm) were retrieved. Microscopic assessment showed an erythrocyte-rich thrombus (83.9% of entire thrombus surface) with layers of platelets/fibrin (lines of Zahn: 13.9% fibrin and 38.5% platelet [CD61+]). The immunological profile was dominated by neutrophils (30% MPO+), with neutrophil extracellular traps (NETs) in 1.9% of thrombus surface. T- (CD3+), B-lymphocytes (CD20+), and monocytes/macrophages (CD68+) were rather rare (2.2%, 0.7%, and 2.0% respectively). We found no evidence (0.0%) of hemosiderin and endothelial cells (CD34+). Full clinical recovery occurred prior to discharge. CONCLUSION: This is the first case report of a CVT with histologic assessment of the thrombus retrieved via EVT. Evaluating thrombi in CVT can provide key insights into disease pathophysiology and guide treatment advancements.
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Trombose Intracraniana , Trombose , Trombose Venosa , Feminino , Humanos , Pessoa de Meia-Idade , Células Endoteliais/patologia , Trombectomia , Trombose Intracraniana/complicações , Trombose Intracraniana/diagnóstico por imagem , Trombose Intracraniana/terapia , Trombose Venosa/complicações , Trombose Venosa/diagnóstico por imagem , Trombose Venosa/terapia , FibrinaRESUMO
The t(14;19)(q32;q13) often juxtaposes BCL3 with immunoglobulin heavy chain (IGH) resulting in overexpression of the gene. In contrast to other oncogenic translocations, BCL3 rearrangement (BCL3-R) has been associated with a broad spectrum of lymphoid neoplasms. Here we report an integrative whole-genome sequence, transcriptomic, and DNA methylation analysis of 13 lymphoid neoplasms with BCL3-R. The resolution of the breakpoints at single base-pair revealed that they occur in two clusters at 5' (n=9) and 3' (n=4) regions of BCL3 associated with two different biological and clinical entities. Both breakpoints were mediated by aberrant class switch recombination of the IGH locus. However, the 5' breakpoints (upstream) juxtaposed BCL3 next to an IGH enhancer leading to overexpression of the gene whereas the 3' breakpoints (downstream) positioned BCL3 outside the influence of the IGH and were not associated with its expression. Upstream BCL3-R tumors had unmutated IGHV, trisomy 12, and mutated genes frequently seen in chronic lymphocytic leukemia (CLL) but had an atypical CLL morphology, immunophenotype, DNA methylome, and expression profile that differ from conventional CLL. In contrast, downstream BCL3-R neoplasms were atypical splenic or nodal marginal zone lymphomas (MZL) with mutated IGHV, complex karyotypes and mutated genes typical of MZL. Two of the latter four tumors transformed to a large B-cell lymphoma. We designed a novel fluorescence in situ hybridization assay that recognizes the two different breakpoints and validated these findings in 17 independent tumors. Overall, upstream or downstream breakpoints of BCL3-R are mainly associated with two subtypes of lymphoid neoplasms with different (epi)genomic, expression, and clinicopathological features resembling atypical CLL and MZL, respectively.
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Leucemia Linfocítica Crônica de Células B , Linfoma Difuso de Grandes Células B , Humanos , Leucemia Linfocítica Crônica de Células B/genética , Hibridização in Situ Fluorescente , Translocação Genética , Rearranjo Gênico , Linfoma Difuso de Grandes Células B/genética , Cadeias Pesadas de Imunoglobulinas/genética , Cromossomos Humanos Par 14/genéticaRESUMO
Drug reaction with eosinophilia and systemic symptoms (DRESS) is a severe and potentially life-threatening drug hypersensitivity reaction. The diagnosis and management of DRESS are complicated due to its heterogeneous clinical and pathologic presentations, delayed onset of signs and symptoms, and unpredictable outcome. This retrospective study aimed to analyze cases of DRESS from a single Italian referring tertiary hospital center (Grande Ospedale Metropolitano Niguarda, Milan, Italy) with a focus on clinical features, causative drugs, histopathologic findings, and treatment. We have included 18 of 32 patients with a probable or definite diagnosis of DRESS. The study observed a slight predominance of women, with antimicrobials and allopurinol identified as the main causative drugs. Clinical manifestations varied, with a monomorphic maculopapular eruption being the most common, whereas facial edema and mucosal involvement were less frequently observed. Multiple organs were commonly affected, with liver and kidney involvement being prominent. Cardiac involvement was associated with the severity of eosinophilia. Laboratory evaluations showed elevated eosinophil levels and increased eosinophil cationic protein levels, supporting the role of eosinophils in DRESS pathogenesis. Histopathologic analysis revealed various patterns often coexisting in the same biopsy in 83% of cases, with interface dermatitis being the most frequent, followed by the perivascular pattern and the spongiotic/eczematous pattern. We observed eosinophils in the biopsy samples in about 50% of patients, and the relationship between peripheral eosinophilia and eosinophils in skin biopsies was not significant. In addition to the RegiSCAR score, age may play a role in predicting disease severity, as older patients with lower scores had poorer outcomes. The prognosis of DRESS depended on early identification, discontinuation of the causative agent, and appropriate therapy. Systemic corticosteroids were the primary treatment option.
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Síndrome de Hipersensibilidade a Medicamentos , Eosinofilia , Humanos , Feminino , Masculino , Síndrome de Hipersensibilidade a Medicamentos/diagnóstico , Síndrome de Hipersensibilidade a Medicamentos/etiologia , Estudos Retrospectivos , Eosinofilia/induzido quimicamente , Eosinofilia/complicações , Pele/patologia , PrognósticoRESUMO
Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are severe drug-induced hypersensitivity reactions characterized by widespread epidermal necrosis, mucous membrane erosions, and systemic findings. We have provided our 11-year experience from a Milan, Italy tertiary hospital managing SJS/TEN, evaluating the clinical and histopathologic features plus the impact on mortality. We retrospectively analyzed 28 patients diagnosed with SJS/TEN based on the clinical and histopathologic findings, according to the classification criteria of multiple studies. We assessed the dermatographics, comorbidities, drug history, lesion characteristics, clinical findings, treatments, blood tests, and outcomes. Severity scores (SCORTEN, Re-SCORTEN, ABCD-10) were used for treatment evaluation and mortality prediction. Data were statistically analyzed, and significant factors associated with mortality were identified. We found that among the 28 patients, 89.2% had comorbidities, mainly cardiovascular diseases, and 21.4% had autoimmune disorders. All patients had received systemic therapy (46.6% monotherapy, 53.6% combination therapy), with systemic steroids (71.4%) and intravenous immunoglobulins (67.8%) being common treatments. There were complications, including systemic infections (67.9%) and septic shock (10.7%). The overall mortality rate was 17.8%. The statistical analysis indicated that malignancy, a high ABCD-10 score, and a high neutrophil-to-lymphocyte ratio were significantly associated with mortality. The extent of affected body surface area did not correlate significantly with mortality. This study provides insights into SJS/TEN management, revealing factors influencing mortality in a high-complexity tertiary hospital setting.
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Síndrome de Stevens-Johnson , Humanos , Síndrome de Stevens-Johnson/epidemiologia , Síndrome de Stevens-Johnson/terapia , Síndrome de Stevens-Johnson/complicações , Estudos Retrospectivos , Centros de Atenção Terciária , Imunoglobulinas Intravenosas/uso terapêutico , ComorbidadeRESUMO
OBJECTIVE: Despite an increase in thyroid fine needle aspiration (FNA) and advances in whole slide imaging (WSI) adoption, digital pathology is still considered inadequate for primary diagnosis of these cases. Herein, we aim to validate the utility of WSI in thyroid FNAs employing the Delphi method strategy. METHODS: A panel of experts from seven reference cytology centres was recruited. The study consisted of two consecutive rounds: (1) an open-ended, free-response questionnaire generating a list of survey items; and (2) a consensus analysis of 80 selected shared WSIs from 80 cases by six investigators answering six morphological questions utilising a 1 to 5 Likert scale. RESULTS: High consensus was achieved for all parameters, with an overall average score of 4.27. The broad majority of items (84%) were ranked either 4 or 5 by each physician. Two badly scanned cases were responsible for more than half of the low-ranked (≤2) values (57%). Good to excellent (≥3) diagnostic confidence was reached in more than 95.2% of cases. For most cases (78%) WSI assessment was not limited by technical issues linked to the image acquisition process. CONCLUSION: This systematic Delphi study indicates broad consensus among participating physicians on the application of DP to thyroid cytopathology, supporting expert opinion that WSI is reliable and safe for primary diagnostic purposes.
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[This corrects the article DOI: 10.3389/fonc.2022.1030232.].
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BACKGROUND: Cancers of the Vater ampulla (ampullary cancers, ACs) account for less than 1% of all gastrointestinal tumors. ACs are usually diagnosed at advanced stage, with poor prognosis and limited therapeutic options. BRCA2 mutations are identified in up to 14% of ACs and, differently from other tumor types, therapeutic implications remain to be defined. Here, we report a clinical case of a metastatic AC patient in which the identification of a BRCA2 germline mutation drove a personalized multimodal approach with curative-intent. CASE PRESENTATION: A 42-year-old woman diagnosed with stage IV BRCA2 germline mutant AC underwent platinum-based first line treatment achieving major tumor response but also life-threatening toxicity. Based on this, as well as on molecular findings and expected low impact of available systemic treatment options, the patient underwent radical complete surgical resection of both primary tumor and metastatic lesions. Following an isolated retroperitoneal nodal recurrence, given the expected enhanced sensitivity to radiotherapy in BRCA2 mutant cancers, the patient underwent imaging-guided radiotherapy leading to long-lasting complete tumor remission. After more than 2 years, the disease remains radiologically and biochemically undetectable. The patient accessed a dedicated screening program for BRCA2 germline mutation carriers and underwent prophylactic bilateral oophorectomy. CONCLUSIONS: Even considering the intrinsic limitations of a single clinical report, we suggest that the finding of BRCA germline mutations in ACs should be taken into consideration, together with other clinical variables, given their potential association with remarkable response to cytotoxic chemotherapy that might be burdened with enhanced toxicity. Accordingly, BRCA1/2 mutations might offer the opportunity of personalizing treatment beyond PARP inhibitors up to the choice of a multimodal approach with curative-intent.
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Adenocarcinoma , Ampola Hepatopancreática , Neoplasias Pancreáticas , Feminino , Humanos , Adulto , Genes BRCA2 , Neoplasias Pancreáticas/genética , Adenocarcinoma/genética , Adenocarcinoma/terapia , Terapia Combinada , Proteína BRCA2/genética , Neoplasias PancreáticasRESUMO
Adverse cutaneous reactions after COVID-19 vaccinations have increased, highlighting not only how SARS-CoV-2 infection but also COVID-19 vaccines may induce adverse cutaneous manifestations. We evaluated the clinical and pathologic spectrum of mucocutaneous reactions after COVID-19 vaccinations, observed consecutively within three large tertiary centers of the Metropolitan City of Milan (Lombardy), comparing our results with the currently available literature. We retrospectively reviewed medical records and skin biopsies of patients diagnosed with mucocutaneous adverse events after COVID-19 vaccinations and followed at three Italian tertiary referral centers in the Metropolitan City of Milan. One hundred twelve patients (77 women and 35 men (112 total); median age, 60 years) have been included in the present study; a cutaneous biopsy was performed in 41 cases (36%). The trunk and arms were the most involved anatomic areas. Autoimmune reactions after COVID-19 vaccinations, urticaria, morbilliform eruptions, and eczematous dermatitis have been the most commonly diagnosed disorders. Compared to the currently available literature, we performed many more histologic examinations, allowing us to make more precise diagnoses. Most of the cutaneous reactions were self-healing and/or responded to topical and systemic steroids and systemic antihistamines, thus not discouraging the general population from carrying out vaccinations, which currently have a good safety profile.
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Vacinas contra COVID-19 , COVID-19 , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , COVID-19/epidemiologia , COVID-19/prevenção & controle , Vacinas contra COVID-19/efeitos adversos , Estudos Retrospectivos , SARS-CoV-2 , Centros de Atenção Terciária , VacinaçãoRESUMO
Mismatch repair (MMR) protein expression in colorectal cancer (CRC) cells is usually homogeneously retained or lost. Rare lesions may show a heterogeneous pattern of MMR protein expression. We evaluated MMR protein expression (MLH1, MSH2, MSH6, and PMS2) in 200 CRCs, identifying 3 groups with proficient MMR protein expression (MMRp), deficient MMR protein expression (MMRd), and heterogeneous MMR protein expression (MMRh). MMRh tumors were microdissected on the basis of the expression of the heterogeneous marker. DNA was extracted and subjected to targeted sequencing. RNA was purified from bulk tumors of all MMRh cases and in a control series of 15 MMRp and 10 MMRd CRCs and analyzed using the PanCancer IO 360 Panel (NanoString Technologies). Twenty-nine of the 200 cases (14.5%) were MMRd. Nine cases (4.5%) showed a heterogeneous pattern of MMR expression, with 6 tumors harboring concomitant loss of one of the other MMR proteins, thus featuring areas with double loss at immunohistochemistry (IHC) testing (MMRh double-loss cases). Four of the 6 MMRh double-loss cases were suitable for a separate sequence variant analysis of IHC double-negative and IHC single-negative components of the tumor. In all lesions, both components exhibited a high tumor mutation burden (TMB). Nevertheless, a significant increase in TMB in the double-negative components was observed (mean TMB: negative, 70 mut/Mb vs positive, 59 mut/Mb) because of a higher number of subclonal variants compared with the other component. Comparative gene expression analyses among MMRd, MMRp, and MMRh CRCs highlighted differential gene expression patterns and an increased number of tumor-infiltrating lymphocytes in MMRh lesions, which is also characterized by a substantial population of exhausted CD8+ lymphocytes. We describe a unique subgroup of CRCs showing heterogeneous expression of MMR proteins in a background of concomitant loss of one of the other markers.