The RNA binding proteins RBM binding motif protein 38 (RBM38) and DEAD END 1 (DND1) selectively stabilize mRNAs by attenuating RNAse activity or protecting them from micro(mi)RNA-mediated cleavage. Furthermore, both proteins can efficiently stabilize the mRNA of the cell cycle inhibitor p21 CIP1 . Since acute myeloid leukemia (AML) differentiation requires cell cycle arrest and RBM38 as well as DND1 have antiproliferative functions, we hypothesized that decreased RBM38 and DND1 expression may contribute to the differentiation block seen in this disease. We first quantified RBM38 and DND1 mRNA expression in clinical AML patient samples and CD34 + progenitor cells and mature granulocytes from healthy donors. We found significantly lower RBM38 and DND1 mRNA levels in AML blasts and CD34 + progenitor cells as compared to mature neutrophils from healthy donors. Furthermore, the lowest expression of both RBM38 and DND1 mRNA correlated with t(8;21). In addition, neutrophil differentiation of CD34 + cells in vitro with G-CSF (granulocyte colony stimulating factor) resulted in a significant increase of RBM38 and DND1 mRNA levels. Similarly, neutrophil differentiation of NB4 acute promyelocytic leukemia (APL) cells was associated with a significant induction of RBM38 and DND1 expression. To address the function of RBM38 and DND1 in neutrophil differentiation, we generated two independent NB4_RBM38 as well as DND1 knockdown cell lines. Inhibition of both RBM38 and DND1 mRNA significantly attenuated NB4 differentiation and resulted in decreased p21 CIP1 mRNA expression. Our results clearly indicate that expression of the RNA binding proteins RBM38 and DND1 is repressed in primary AML patients, that neutrophil differentiation is dependent on increased expression of both proteins, and that these proteins have a critical role in regulating p21 CIP1 expression during APL differentiation. Highlights RBM38 and DND1 expression is attenuated in primary AML patients  Normal and leukemic neutrophil differentiation induces RBM38 and DND1 expression  New function for the RNA binding proteins RBM38 and DND1 in APL differentiation Keywords: RBM38, DND1, acute myeloid leukemia, acute promyelocytic leukemia, neutrophil differentiation

Ovarian clear cell carcinoma (OCCC) is a rare subtype of epithelial ovarian cancer characterised by a high frequency of loss-of-function ARID1A mutations and a poor response to chemotherapy. Despite their generally low mutational burden, an intratumoural T cell response has been reported in a subset of OCCC, with ARID1A purported to be a biomarker for the response to the immune checkpoint blockade independent of micro-satellite instability (MSI). However, assessment of the different immune cell types and spatial distribution specifically within OCCC patients has not been described to date. Here, we characterised the immune landscape of OCCC by profiling a cohort of 33 microsatellite stable OCCCs at the genomic, gene expression and histological level using targeted sequencing, gene expression profiling using the NanoString targeted immune panel, and multiplex immunofluorescence to assess the spatial distribution and abundance of immune cell populations at the protein level. Analysis of these tumours and subsequent independent validation identified an immune-related gene expression signature associated with risk of recurrence of OCCC. Whilst histological quantification of tumour-infiltrating lymphocytes (TIL, Salgado scoring) showed no association with the risk of recurrence or ARID1A mutational status, the characterisation of TILs via multiplexed immunofluorescence identified spatial differences in immunosuppressive cell populations in OCCC. Tumour-associated macrophages (TAM) and regulatory T cells were excluded from the vicinity of tumour cells in low-risk patients, suggesting that high-risk patients have a more immunosuppressive microenvironment. We also found that TAMs and cytotoxic T cells were also excluded from the vicinity of tumour cells in ARID1A-mutated OCCCs compared to ARID1A wild-type tumours, suggesting that the exclusion of these immune effectors could determine the host response of ARID1A-mutant OCCCs to therapy. Overall, our study has provided new insights into the immune landscape and prognostic associations in OCCC and suggest that tailored immunotherapeutic approaches may be warranted for different subgroups of OCCC patients.

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Successful myeloid differentiation depends on the expression of a series of miRNAs. Thus, it is hardly surprising that miRNAs are globally repressed in AML, a disease mainly characterized by a block in cellular myeloid differentiation. Studies investigating the mechanisms for low miRNA expression in AML has mostly focused on altered transcriptional regulation or deletions, whereas defective miRNA processing has received less attention. In this study, we report that the expression of the key miRNA processing enzyme DICER1 is down-regulated in primary AML patient samples and healthy CD34(+) progenitor cells as compared with granulocytes. In line with these findings, Dicer1 expression was induced significantly in AML cell lines upon neutrophil differentiation. The knocking down of DICER1 in AML cells significantly attenuated neutrophil differentiation, which was paralleled by decreased expression of miRNAs involved in this process. Moreover, we found that inhibiting DICER1 attenuated the activation of autophagy, a cellular recycling process that is needed for proper neutrophil differentiation of AML cells. Our results clearly indicate that DICER1 plays a novel role in neutrophil differentiation as well as in myeloid autophagy of AML cells.

Purpose Our aim is to describe the role of immune checkpoint inhibitors (ICI) in clinical practice by providing the patient and tumor characteristics as well as survival and toxicity rates by sex. Methods We used electronic health records to identify patients treated at the Cancer Center of the University Hospital Bern, Switzerland between January 1, 2017 and June 16, 2021. Results We identified 5109 patients, 689 of whom (13.5%) received at least one dose of ICI. The fraction of patients who were prescribed ICI increased from 8.6% in 2017 to 22.9% in 2021. ICI represented 13.2% of the anticancer treatments in 2017 and increased to 28.2% in 2021. The majority of patients were male (68.7%), who were older than the female patients (median age 67 vs. 61 years). Over time, adjuvant and first line treatments increased for both sexes. Lung cancer and melanoma were the most common cancer types in males and females. The incidence of irAEs was higher among females (38.4% vs. 28.1%) and lead more often to treatment discontination in females than in males (21.1% vs. 16.8%). Independent of sex, the occurrence of irAEs was associated with greater median overall survival (OS, not reached vs. 1.1 years). Female patients had a longer median OS than males (1.9 vs. 1.5 years). Conclusions ICI play an increasingly important role in oncology. irAEs are more frequent in female patients and are associated with a longer OS. More research is needed to understand the association between patient sex and toxicity and survival.

e18770 Background: Maintenance therapy with PARP inhibitors (PARPi) in recurrent high grade ovarian cancer is standard of care for patients who have responded to second or subsequent lines of platinum-based chemotherapy. The increased access to PARP inhibitors (Olaparib, Niraparib and Rucaparib) has provided the opportunity to explore the real-world toxicities in routine clinical practice, toxicity management and the consequent impact on maintenance therapy outcomes. Methods: Patients with relapsed ovarian cancer that received maintenance PARP inhibitor therapy in routine clinical practice between April 2015 and April 2020 were identified. Electronic patient records were reviewed retrospectively to retrieve details of any reported toxicities (occurring at any time during therapy) and their management. Data was entered into and analysed in a Microsoft Excel spreadsheet. Results: 99 patients who received second or subsequent line maintenance PARPi therapy were included (median age 63.6 years). 36% had a germline BRCA1/2 mutation, 6% had a somatic BRCA1/2 mutation and 58% were BRCA wild-type. 69% received 2nd line maintenance therapy; 22% and 9% received a maintenance PARP inhibitor following 3rd or 4+ line therapy respectively. 56% had not received previous maintenance therapy; 43% had received Bevacizumab. 48% patients commenced maintenance therapy at full dose. 13% of patients experienced no toxicities. 60% of patients experienced G1-2 toxicities, with 42% experiencing >2 episodes; most common toxicities were fatigue, nausea/vomiting and thrombocytopenia. 26% of patients experienced >G3 toxicity, with 9% experiencing >2 episodes, 4% of which were recurring toxicities; most common toxicities were hypertension, neutropenia and anaemia. 64% of patients developed toxicity within the first cycle of treatment; 39% had a dose interruption, 56% of which were < 2 weeks duration. 59% patients required a dose reduction from their starting dose due to toxicities. There was no significant difference in median PFS between patients who had been dose reduced compared to those who received full starting dose (p > 0.05). Conclusions: In keeping with phase III clinical trials, our real-world experience is that most PARPi toxicities are low grade and occur early in treatment. Toxicities can be effectively managed with brief dose interruptions and dose reductions, without adverse impact on survival outcomes.

ObjectiveTo investigate whether a change in the Fagotti score (ΔFagotti) following neoadjuvant chemotherapy is predictive of resection to no residual disease (R0) and survival in women diagnosed with ovarian cancer.MethodsWomen treated with neoadjuvant chemotherapy for newly diagnosed ovarian cancer between January 2012 and June 2021 at the Bern University Hospital were included in this retrospective cohort study. Fagotti scores before and after neoadjuvant chemotherapy treatment were assessed for a potential association with resection status at interval debulking surgery defined as no residual disease (R0), macroscopic residual disease with a diameter of 0.1–1 cm (R1) or >1 cm (R2), and survival.ResultsDuring the study period, 130 patients received neoadjuvant chemotherapy, mainly in response to advanced ovarian cancer International Federation of Gynecology and Obstetrics (FIGO) stages IIIC (68.5%) or IV (20.8%). 91 patients (70%) experienced a relapse and 81 (62%) died due to their disease. Median overall survival was 40 months (95% CI 30.6 to 49.4). Fagotti scores dropped from a mean of 7.8 (95% CI 7.14 to 8.42) at diagnosis to 3.9 (95% CI 3.34 to 4.46, p<0.001) after neoadjuvant therapy. This decrease was associated with resection status during interval debulking surgery (mean ΔFagotti −4.9 in R0, −2.2 in R1, −0.6 in R2, p<0.001). Women whose Fagotti score declined more than 2 points after neoadjuvant chemotherapy (n=51/88, 58%) survived significantly longer (median overall survival of 42 vs 32 months, p=0.048).ConclusionFagotti scores and ΔFagotti scores are associated with complete cytoreduction at interval debulking surgery and longer overall survival in women treated with neoadjuvant chemotherapy for ovarian cancer. These markers are valuable for individualized patient treatment planning and should always be performed after neoadjuvant therapy.