Ultrasonography-guided core-needle biopsy of lymphadenopathies suspected of lymphoma: Analysis on diagnostic efficacy and safety of 1000 front-line biopsies in a multicenter Italian study.

The reliability and safety of front-line ultrasonography guided core needle biopsy (UG-CNB) performed with specific uniform approach have never been evaluated in a large series of patients with lymphadenopathies suspected of lymphoma. The aim of this study was to assess the overall accuracy of UG-CNB in the lymph node histological diagnosis, using a standard reference based on pathologist consensus, molecular biology, and/or surgery. We retrospectively checked the findings concerning the application of lymph node UG-CNB from four Italian clinical units that routinely utilized 16-gauge diameter modified Menghini needle under power-Doppler ultrasonographic guidance. A data schedule was sent to all centers to investigate the information regarding techniques, results, and complications of lymph node UG-CNB in untreated patients over a 12-year period. Overall, 1000 (superficial target, n = 750; deep-seated target, n = 250) biopsies have been evaluated in 1000 patients; other 48 biopsies (4.5%), screened in the same period, were excluded because inadequate for a confident histological diagnosis. Most patients were suffering from lymphomas (aggressive B-cell non-Hodgkin lymphoma [aBc-NHL], 309 cases; indolent B-cell [iBc]-NHL, 279 cases; Hodgkin lymphoma [HL], 212 cases; and nodal peripheral T-cell [NPTC]-NHL, 30 cases) and 100 cases from metastatic carcinoma; 70 patients had non-malignant disorders. The majority of CNB results met at least one criterion of the composite reference standard. The overall accuracy of the micro-histological sampling was 97% (95% confidence interval: 95%-98%) for the series. The sensitivity of UG-CNB for the detection of aBc-NHL was 100%, for iBc-NHL 95%, for HL 93%, and for NPTC-NHL 90%, with an overall false negative rate of 3.3%. The complication rate was low (6% for all complications); no patient suffered from biopsy-related complications of grade >2 according to the Common Terminology Criteria for Adverse Events. Lymph node UG-CNB as mini-invasive diagnostic procedure is effective with minimal risk for the patient.

TCGA Molecular Prognostic Groups of Endometrial Carcinoma: Current Knowledge and Future Perspectives.

The four TCGA-based molecular prognostic groups of endometrial carcinoma (EC), i.e., POLE-mutant, mismatch repair (MMR)-deficient, p53-abnormal, and "no specific molecular profile" (NSMP), have recently been integrated into ESGO-ESTRO-ESP guidelines. The POLE-mutant and MMR-deficient groups are associated with high mutational load, morphological heterogeneity, and inflammatory infiltration. These groups are frequent in high-grade endometrioid, undifferentiated/dedifferentiated, and mixed histotypes. POLE-mutant ECs show good prognosis and do not require adjuvant treatment, although the management of cases at stage >II is still undefined. MMR-deficient ECs show intermediate prognosis and are currently substratified based on clinicopathological variables, some of which might not have prognostic value. These groups may benefit from immunotherapy. P53-mutant ECs are typically high-grade and often morphologically ambiguous, accounting for virtually all serous ECs, most carcinosarcomas and mixed ECs, and half of clear-cell ECs. They show poor prognosis and are treated with chemoradiotherapy; a subset may benefit from HER2 inhibitors or PARP inhibitors. The NSMP group is the most frequent TCGA group; its prognosis is highly variable and affected by clinicopathological/molecular factors, most of which are still under evaluation. In conclusion, the TCGA classification has improved diagnosis, risk stratification, and management of EC. Further studies are needed to resolve the points of uncertainty that still exist.

Primary cutaneous anaplastic large-cell lymphoma of the eyelid: report of two cases and review of the literature.

PURPOSE: Two new cases of primary cutaneous CD30+ anaplastic large-cell lymphoma (cALCL) of the eyelid are reported; these are analysed alongside existing cases to identify challenges relating to the diagnosis and management of such rare lesions. MATERIAL AND METHODS: A review of existing literature on the PubMed database is conducted using the keywords: 'eyelid lymphoid proliferations', 'lymphoma of the eyelid', and 'primary cutaneous CD30+, ALK-anaplastic large-cell lymphoma of the eyelid'. Two new cases of cALCL are reported. Cases where patients present solely with a nodular periocular lesion are analysed for recurrence and survival rate. RESULTS: Two new patients with a painless ulcerated nodule on the upper eyelid receive a confirmed diagnosis of cALCL after undergoing an excisional biopsy. The first, elderly patient has spontaneous remission; the second patient, with a concomitant chronic infection of hepatitis C virus (HCV), presents a more diffuse disease at the onset and requires radiotherapy. Together with 13 patients a primary cALCL identified from 11 previous studies, this constitutes a cohort of 15 patients. Of these, 10 present with an exclusively nodular lesion of the eyelid and four experience disease recurrence; no deaths from cALCL are reported. CONCLUSION: Differential diagnosis between primary cALCL and lymphomatoid papulosis is essential and requires careful consideration of clinical and pathologic features. Radiologic staging examination is crucial in order to exclude systemic ALCL, particularly for patients with comorbidity. Though cALCL has the pathological features of a malignant lesion, the prognosis seems favourable for patients; a relatively high percentage even experience spontaneous resolution.

TBX1 and Basal Cell Carcinoma: Expression and Interactions with Gli2 and Dvl2 Signaling.

Early events of basal cell carcinoma (BCC) tumorigenesis are triggered by inappropriate activation of SHH signaling, via the loss of Patched1 (Ptch1) or by activating mutations of Smoothened (Smo). TBX1 is a key regulator of pharyngeal development, mainly through expression in multipotent progenitor cells of the cardiopharyngeal lineage. This transcription factor is connected to several major signaling systems, such as FGF, WNT, and SHH, and it has been linked to cell proliferation and to the regulation of cell shape and cell dynamics. Here, we show that TBX1 was expressed in all of the 51 BCC samples that we have tested, while in healthy human skin it was only expressed in the hair follicle. Signal intensity and distribution was heterogeneous among tumor samples. Experiments performed on a cellular model of mouse BCC showed that Tbx1 is downstream to GLI2, a factor in the SHH signaling, and that, in turn, it regulates the expression of Dvl2, which encodes an adaptor protein that is necessary for the transduction of WNT signaling. Consistently, Tbx1 depletion in the cellular model significantly reduced cell migration. These results suggest that TBX1 is part of a core transcription network that promotes BCC tumorigenesis.

Borrelia burgdorferi in primary cutaneous lymphomas: a systematic review and meta-analysis.

BACKGROUND: The association between Borrelia burgdorferi and primary cutaneous lymphoma is still unclear. This systematic review and meta-analysis aims to define the association of Borrelia burgdorferi with primary cutaneous lymphoma and its different entities. METHODS: Electronic databases were searched for all studies that assessed the presence of Borrelia burgdorferi DNA in specimens of primary cutaneous lymphoma. The association between Borrelia and primary cutaneous lymphomas was assessed with an odds ratio (significant p < 0.05); cutaneous specimens with no lymphoproliferative disorders were used as controls. A secondary analysis was performed to assess the prevalence of Borrelia infection in different lymphoma entities. RESULTS: Ten studies with 506 primary cutaneous lymphomas and 201 controls were included. The prevalence of Borrelia DNA positivity was highly heterogeneous among studies from different regions. Borrelia DNA positivity was significantly associated with primary cutaneous lymphomas (odds ratio = 10.88; p < 0.00001). The prevalence of Borrelia DNA positivity was similar among different entities (marginal zone: 7.3 %; follicular: 8.1 %; diffuse large B-cell: 7.5 %; mycosis fungoides: 8 %). CONCLUSIONS: Borrelia burgdorferi is significantly associated with primary cutaneous lymphomas, with no differences among the several lymphoma entities (both B-cell and T-cell), but with strong geographical differences. Molecular testing for Borrelia would be justified in patients with primary cutaneous lymphoma from endemic areas.

Cutaneous localization of plasmablastic multiple myeloma with heterotopic expression of CD3 and CD4: Skin involvement revealing systemic disease.

Plasmablastic multiple myeloma is an uncommon morphological variant of multiple myeloma with aggressive clinical course and poor outcome. Its differential diagnosis includes plasmablastic lymphoma, a variant of diffuse large B-cell lymphoma with frequent extranodal presentation, which usually affects immunosuppressed patients and is virtually indistinguishable from plasmablastic multiple myeloma on the basis of histology solely. Differential diagnosis relies on close clinical-pathological correlation. Herein, the authors report a case of aggressive multiple myeloma occurring in a 48-year-old patient with pure plasmablastic morphology, expression of T-cell markers CD3 and CD4, and cutaneous involvement as first presenting sign. Heterotopic expression of T-cell markers has been described in literature for both plasmablastic multiple myeloma and plasmablastic lymphoma. The causative mechanisms underlying this aberrant phenotype have not yet been elucidated; nevertheless the possibility of this rare finding should be considered to avoid misinterpretations. Remarkably, despite occurring rarely, cutaneous involvement could be observed at an early stage or even be the first manifestation of disease in particularly aggressive forms of myeloma. As a consequence, the presence of cutaneous lesions should not favor a straightforward diagnosis of plasmablastic lymphoma. The importance of a correct differential diagnosis lies in its therapeutical implications.

HPV Virus Transcriptional Status Assessment in a Case of Sinonasal Carcinoma.

Human Papilloma Virus (HPV) can play a causative role in the development of sinonasal tract malignancies. In fact, HPV may be the most significant causative agent implicated in sinonasal tumorigenesis and is implicated in as many as 21% of sinonasal carcinomas. To date, there are no definitive, reliable and cost-effective, diagnostic tests approved by the FDA for the unequivocal determination of HPV status in head and neck cancers. We followed an exhaustive algorithm to correctly test HPV infection, including a sequential approach with p16INK4a IHC, viral DNA genotyping and in situ hybridization for E6/E7 mRNA. Here, we report a case of sinonasal carcinoma with discordant results using HPV test assays. The tumor we describe showed an irregular immunoreactivity for p16INK4a, and it tested positive for HPV DNA; nevertheless, it was negative for HR-HPV mRNA. We discuss the possible meaning of this discrepancy. It would be advisable to test HPV transcriptional status of sinonasal carcinoma on a diagnostic routine basis, not only by p16INK4a IHC assay, but also by HPV DNA genotyping and HR-HPV mRNA assessment.

FKBP51 Immunohistochemical Expression: A New Prognostic Biomarker for OSCC?

Up-to-date, several molecular markers of prognosis have been studied in Oral Squamous Cell Carcinoma (OSCC), but none entered in the clinical setting. Therapy of OSCC tumors mainly relies on surgery, radiotherapy and partially on chemotherapy; there is an urgent need for biomarkers able to better stratify OSCC patients' risk to address targeted therapeutic strategies. The role of immune response in the pathogenesis and biological behavior of OSCC has been investigated by several authors, and promising results have been obtained with immune checkpoint inhibitors. We already investigated the role of the immune modulator FK506-binding protein 51 (FKBP51), a FK506-binding immunophilin, in cutaneous melanoma biology, and its expression in several human solid tumors. In the present study, we aimed to assess the value of FKBP51 expression in OSCC tumor cells as a marker of outcome. We collected clinical data from 72 patients who underwent surgery for Squamous Cell Carcinoma (SCC) of the tongue, floor, lips and palate. FKBP51 expression was assessed by immunohistochemistry on paraffin-embedded tumor tissues. In addition, we evaluated the human papillomavirus (HPV) status of primary tumors by immunohistochemistry, viral subtyping and In Situ Hybridization (ISH) assay. We found that high FKBP51-expressing tumors characterized the OSCCs with the worst prognosis: the high immunohistochemical expression of FKBP51 associated with death occurring within five years from the diagnosis with a sensitivity of 88.46% and a specificity of 91.67%. The estimated positive predictive value of the test was 88.45% and negative predictive value 91.67%. We tested FKBP51 mRNA presence, by RT-PCR assay, in a selected series of OSCC tumors, and we found that mRNA correlated well to the protein expression and to the clinical outcome. Applying the Bayes formula, we estimated an 88% probability of dying within five years from the diagnosis of OSCC patients with a high FKBP51 immunohistochemical (IHC) test result (>51% of FKBP51 positive tumor cells). On the basis of our analysis, we propose tumor tissue expression of FKBP51 protein as a reliable prognostic marker for OSCC tumors.

A deep learning model to predict Ki-67 positivity in oral squamous cell carcinoma.

Anatomical pathology is undergoing its third revolution, transitioning from analogical to digital pathology and incorporating new artificial intelligence technologies into clinical practice. Aside from classification, detection, and segmentation models, predictive models are gaining traction since they can impact diagnostic processes and laboratory activity, lowering consumable usage and turnaround time. Our research aimed to create a deep-learning model to generate synthetic Ki-67 immunohistochemistry from Haematoxylin and Eosin (H&E) stained images. We used 175 oral squamous cell carcinoma (OSCC) from the University Federico II's Pathology Unit's archives to train our model to generate 4 Tissue Micro Arrays (TMAs). We sectioned one slide from each TMA, first stained with H&E and then re-stained with anti-Ki-67 immunohistochemistry (IHC). In digitised slides, cores were disarrayed, and the matching cores of the 2 stained were aligned to construct a dataset to train a Pix2Pix algorithm to convert H&E images to IHC. Pathologists could recognise the synthetic images in only half of the cases in a specially designed likelihood test. Hence, our model produced realistic synthetic images. We next used QuPath to quantify IHC positivity, achieving remarkable levels of agreement between genuine and synthetic IHC. Furthermore, a categorical analysis employing 3 Ki-67 positivity cut-offs (5%, 10%, and 15%) revealed high positive-predictive values. Our model is a promising tool for collecting Ki-67 positivity information directly on H&E slides, reducing laboratory demand and improving patient management. It is also a valuable option for smaller laboratories to easily and quickly screen bioptic samples and prioritise them in a digital pathology workflow.

Case report: Potential role of immunotherapy in thymic malignancies: a unique case of a durable and complete response upon an immune checkpoint inhibitor.

Thymic epithelial tumors are rare malignancies with an incidence of 1.7 cases per million people per year. They pose significant management challenges due to their association with autoimmune disorders. In this case report, we present the 21-year history of a patient diagnosed with advanced B2/B3 thymoma and Good's syndrome. The patient achieved a complete and durable response after receiving only two cycles of the immune checkpoint inhibitor Nivolumab. However, this positive outcome was accompanied by the development of severe immune-related myocarditis complicated by reactivation of cytomegalovirus. Moreover, the patient developed a highly uncommon subdiaphragmatic pararectal dissemination of the thymic tumor, which is a condition rarely described in the literature. Despite the success in achieving complete and durable response with immune checkpoint inhibitors, the emergence of immune-related adverse events highlights the potential challenges associated with these treatments, emphasizing the need for careful monitoring and a comprehensive understanding of the intricate interplay between cancer, immune system dysregulations and immunotherapy.

Small-Cell Carcinoma of Nasopharynx: A Case Report of Unusual Localization.

Neuroendocrine tumors are a spectrum of rare and highly heterogeneous neoplasms with distinct functional and biological behavior in relation to location, tumor size, and histological differentiation. Neuroendocrine tumors arise from the neuroendocrine cells of the diffuse neuroendocrine system located in almost every organ. Neuroendocrine tumors in the head and neck district are usually reported in sinonasal cavities and larynx. We present the case of a nasopharyngeal small-cell neuroendocrine carcinoma, which, as far as we know, is the 16th case reported in literature.

Granuloma annulare after SARS-CoV-2 vaccination: A case report and a literature review.

INTRODUCTION: During the Cov-19 pandemic, many studies reported a broad spectrum of cutaneous reactions presenting as erythematous rashes or pernio-like, urticaria-like or vesicular/bullous patterns associated with Cov-19-infection and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination. METHODS: The authors documented the clinical and histopathological features of an unexpected case of granuloma annulare (GA) arising a few days after the SARS-CoV-2 vaccination and reviewed all GAs reported in the literature following the SARS-CoV-2 vaccination and Cov-19-infection. CASE REPORT: A 69-year-old woman developed a single reddish lesion on the left deltoid region, where the SARS-CoV-2 vaccine seven days earlier was injected. The clinicians performed a punch skin biopsy, and histology revealed an interstitial GA. CONCLUSIONS: Clinicians should be aware of the potential, though rare, GA occurrence as a possible adverse event after the SARS-CoV-2 vaccination. This additional case, like what happens after the administration of other vaccines, supports the idea that GA may result from the immune system activation following the vaccination. However, notwithstanding, they should encourage their patients to obtain immunization to assist the public health systems in overcoming the COVID-19 pandemic.

Immunohistochemical expression of PRAME is a marker of poor prognosis in uveal melanoma: A clinico-pathologic and immunohistochemical study on a series of 85 cases.

PReferentially expressed Antigen in Melanoma (PRAME) is a cancer testis antigen, first isolated in tumor-reactive T-cell clones from a metastatic melanoma patient. It has been widely studied in skin pathology as an immunohistochemical marker capable of distinguishing between benign nevi and malignant melanomas. PRAME has been found to be also expressed in non-melanocytic tumors, including lung, breast, kidney and ovarian cancer. However, less is known about the diagnostic and/or prognostic role of this protein in uveal melanoma (UM); few studies have reported that PRAME expression seems to give to UM patients an additional metastatic risk beyond the other already-known prognostic parameters. In the present retrospective study, we aimed to correlate PRAME immunoreactivity to other clinico-pathologic features and follow-up data on a large series of 85 cases (45 non-metastasizing and 40 metastasizing tumors) of primary UM. A statistically significant correlation was found between PRAME expression and higher metastatic risk and lower metastasis-free survival. We propose to include PRAME in the immunohistochemical panel of UM as an easily usable marker capable of predicting higher metastatic risk and stratifying patients' outcome.

Diagnostic accuracy of HIK1083 and MUC6 as immunohistochemical markers of endocervical gastric-type adenocarcinoma: A systematic review and meta-analysis.

INTRODUCTION: HIK1083 and MUC6 have been used as immunohistochemical markers to differentiate gastric-type adenocarcinoma (GTAC) from other endocervical adenocarcinomas. We aimed to assess their diagnostic accuracy through a systematic review and meta-analysis. METHODS: Three electronic databases were searched from their inception to July 2022 for all studies assessing the expression in endocervical GTAC vs other endocervical adenocarcinomas. Diagnostic accuracy was assessed as sensitivity, specificity, positive likelihood ratio (LR+), negative likelihood ratio (LR-), diagnostic odds ratio (DOR), and area under the curve (AUC) on SROC curves. RESULTS: Four studies with 343 patients were included. HIK1083 showed sensitivity= 0.64, specificity= 0.94, LR+ =8.30, LR-= 0.38, DOR= 33.36, AUC= 89.9%. MUC6 showed sensitivity= 0.51, specificity= 0.74, LR+ =1.96, LR-= 0.71, DOR= 3.48, AUC= 72.8%. CONCLUSION: HIK1083 showed high specificity and low sensitivity as a marker of GTAC, with moderate overall accuracy; MUC6 showed moderate specificity and low sensitivity, with low overall accuracy.

Autoimmune mucocutaneous blistering diseases after SARS-Cov-2 vaccination: A Case report of Pemphigus Vulgaris and a literature review.

BACKGROUND: Cases of severe autoimmune blistering diseases (AIBDs) have recently been reported in association with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination. AIMS: To describe a report of oropharyngeal Pemphigus Vulgaris (OPV) triggered by the mRNABNT162b2 vaccine (Comirnaty®/ Pfizer/ BioNTech) and to analyze the clinical and immunological characteristics of the AIBDs cases reported following the SARS-CoV-2 vaccination. METHODS: The clinical and immunological features of our case of OPV were documented. A review of the literature was conducted and only cases of AIBDs arising after the SARS-CoV-2 vaccination were included. CASE REPORT: A 60-year old female patients developed oropharyngeal and nasal bullous lesions seven days after the administration of a second dose of the mRNABNT162b2 vaccine (Comirnaty®/ Pfizer/BioNtech). According to the histology and direct immunofluorescence findings showing the presence of supra-basal blister and intercellular staining of IgG antibodies and the presence of a high level of anti-Dsg-3 antibodies (80 U/ml; normal < 7 U/ml) in the serum of the patients, a diagnosis of oropharyngeal Pemphigus Vulgaris was made. REVIEW: A total of 35 AIBDs cases triggered by the SARS-CoV-2 vaccination were found (including our report). 26 (74.3%) were diagnosed as Bullous Pemphigoid, 2 (5.7%) as Linear IgA Bullous Dermatosis, 6 (17.1%) as Pemphigus Vulgaris and 1 (2.9%) as Pemphigus Foliaceus. The mean age of the sample was 72.8 years and there was a predominance of males over females (F:M=1:1.7). In 22 (62.9%) cases, the disease developed after Pfizer vaccine administration, 6 (17.1%) after Moderna, 3 (8.6%) after AstraZeneca, 3 (8.6%) after CoronaVac (one was not specified). All patients were treated with topical and/or systemic corticosteroids, with or without the addition of immunosuppressive drugs, with a good clinical response in every case. CONCLUSION: Clinicians should be aware of the potential, though rare, occurrence of AIBDs as a possible adverse event after the SARS-CoV-2 vaccination. However, notwithstanding, they should encourage their patients to obtain the vaccination in order to assist the public health systems to overcome the COVID-19 pandemic.

Primary cutaneous B cell lymphoma, leg type presenting as a diabetic ulcer: A challenging diagnosis.

INTRODUCTION: A crescent number of reports describe malignant dermal malignancies presenting as diabetic ulcers, such as melanoma, Kaposi's sarcoma, squamous cell carcinoma and cutaneous lymphoma. METHODS: The authors reported the clinical and histopathological features of this challenging case of a PCBCL, leg type presenting as a foot ulcer to exemplify the diagnostic difficulties, mainly when, at the onset, this tumour exhibits uncharacteristic features. CASE REPORT: A 43 years-old male with a 10-year history of compensated type I diabetes developed an ulcerated 3 cm of diameter tumour on the lateral region of the right foot. This lesion had previously been biopsied and treated as a diabetic neuropathic ulcer elsewhere. Due to the appearance of intralesional necrosis associated with stable inflammation and diabetes laboratory parameters, the clinicians made a provisional clinical diagnosis of pyoderma gangrenosum and performed further two incisional biopsies. Histology showed a clear-cut PCBCL, leg type. CONCLUSIONS: Diabetic skin lesions, especially in older patients with persistent non-healing characteristics of pain and tenderness, must be carefully managed through the close correlation of clinical, imaging, and histological features. A correct diagnosis allows avoiding inadequate treatment, which would lead to severe consequences for these patients.

Prognostic value of Bcl2 and Bcl6 in primary cutaneous large B-cell lymphoma: A systematic review and meta-analysis.

AIMS: To assess the prognostic value of Bcl2 and Bcl6 in primary cutaneous diffuse large B-cell lymphoma (pcDLBCL), through a systematic review and meta-analysis. METHODS: Electronic databases were searched from their inception to April 2021 for studies reporting Bcl2 and Bcl6 expression and survival outcomes in pcDLBCL series. Kaplan-Meier and Cox regression survival analyses with hazard ratio calculation were performed for overall survival (OS), with a significant p-value< 0.05. RESULTS: Eight studies with 148 patients were included. OS was significantly decreased in Bcl2-pos itive pcDLBCLs (5-year OS= 52.9 ± 5.2%) compared to Bcl2 negative pcDLBCLs (5-year OS= 86.6 ± 7.2%), with a HR of 4.615 (95% CI, 1.827-11.657; p = 0.001); no significant difference in OS was found between Bcl6-positive pcDLBCLs (5-year OS= 61.3 ± 6.5%) and Bcl6-negative pcDLBCLs (5-year OS= 56.8 ± 7.2%), with a HR of 0.789 (95% CI, 0.462-1.350; p = 0.388). CONCLUSIONS: In pcDLBCL, Bcl2 expression is a strong unfavourable prognostic marker; Bcl6 does not seem to be associated with survival instead. Further studies are necessary in this field.

The disruption of the CCDC6 - PP4 axis induces a BRCAness like phenotype and sensitivity to PARP inhibitors in high-grade serous ovarian carcinoma.

BACKGROUND: Treatment with PARP inhibitors (PARPi) is primarily effective against high-grade serous ovarian cancers (HGSOC) with BRCA1/2 mutations or other deficiencies in homologous recombination (HR) repair mechanisms. However, resistance to PARPi frequently develops, mostly as a result of BRCA1/2 reversion mutations. The tumour suppressor CCDC6 is involved in HR repair by regulating the PP4c phosphatase activity on γH2AX. In this work, we reported that in ovarian cancer cells, a physical or functional loss of CCDC6 results synthetic lethal with the PARP-inhibitors drugs, by affecting the HR repair. We also unravelled a role for CCDC6 as predictive marker of PARPi sensitivity in ovarian cancer, and the impact of CCDC6 downregulation in overcoming PARPi resistance in these tumours. METHODS: A panel of HGSOC cell lines (either BRCA-wild type or mutant) were treated with PARPi after CCDC6 was attenuated by silencing or by inhibiting USP7, a CCDC6-deubiquitinating enzyme, and the effects on cell survival were assessed. At the cellular and molecular levels, the processes underlying the CCDC6-dependent modification of drugs' sensitivity were examined. Patient-derived xenografts (PDXs) were immunostained for CCDC6, and the expression of the protein was analysed statistically after digital or visual means. RESULTS: HGSOC cells acquired PARPi sensitivity after CCDC6 depletion. Notably, CCDC6 downregulation restored the PARPi sensitivity in newly generated or spontaneously resistant cells containing either wild type- or mutant-BRCA2. When in an un-phosphorylated state, the CCDC6 residue threonine 427 is crucial for effective CCDC6-PP4 complex formation and PP4 sequestration, which maintains high γH2AX levels and effective HR. Remarkably, the PP4-dependent control of HR repair is influenced by the CCDC6 constitutively phosphorylated mutant T427D or by the CCDC6 loss, favouring PARPi sensitivity. As a result, the PP4 regulatory component PP4R3α showed to be essential for both the activity of the PP4 complex and the CCDC6 dependent PARPi sensitivity. It's interesting to note that immunohistochemistry revealed an intense CCDC6 protein staining in olaparib-resistant HGSOC cells and PDXs. CONCLUSIONS: Our findings suggest that the physical loss or the functional impairment of CCDC6 enhances the PP4c complex activity, which causes BRCAness and PARPi sensitivity in HGSOC cells. Moreover, CCDC6 downregulation might overcome PARPi resistance in HGSOCs, thus supporting the potential of targeting CCDC6 by USP7 inhibitors to tackle PARPi resistance.