Highlights d Maintained expression of differentiation factor Ptf1a blocks pancreatic tumorigenesis d Tumor-promoting inflammation cannot overcome Ptf1amediated tumor suppression d Ptf1a expression re-differentiates pancreatic cancer precursors to exocrine cells d Ptf1a expression inhibits growth and clonogenicity of human pancreatic cancer cells

Cytologic diagnosis of metastasis to the pancreas is rare in our institution, comprising only 2.5% and 7.2% of total and malignant pancreatic FNA/CNB, respectively. FNA/CNB with ROSE proved to be an effective diagnostic modality, thereby obviating the need for more invasive procedures in the setting of pancreatic metastases. EUS-FNA was equally effective as CT-guided biopsies in achieving specimen adequacy and definitive diagnoses. We also present the first known case of a metastatic olfactory neuroblastoma to the pancreas diagnosed by imprint cytology.

SUMMARYActivating mutations in Kras are nearly ubiquitous in human pancreatic cancer and initiate precancerous pancreatic intraepithelial neoplasia (PanINs) when induced in adult murine acinar cells. PanINs normally take months to form, but can be rapidly induced by genetic deletion of acinar cell differentiation factors such as Ptf1a, suggesting that loss of mature cell identity is a rate-limiting step in pancreatic tumor initiation. Using a novel genetic mouse model that allows for independent control of oncogenic Kras and Ptf1a expression, we demonstrate that maintained activity of Ptf1a is sufficient to eliminate Kras-driven tumorigenesis, even in the presence of tumor-promoting inflammation. Furthermore, reintroduction of Ptf1a into established PanINs reverts their phenotype in vivo. Our results suggest that reactivation of an endogenous differentiation program can prevent and reverse oncogenesis in cells harboring tumor driving mutations, thus introducing a novel paradigm for solid tumor prevention and treatment.

Background Metastatic tumors to the pancreas are rarely encountered and diagnostically challenging. We aspired to determine the incidence and origin of all metastases to the pancreas at our institution, and to examine their clinicopathologic and cytomorphologic features. We also sought to ascertain the effect of endoscopic ultrasound (EUS) guidance implementation. Methods A search of our database was undertaken to review all pancreatic FNA and/or CNB examined from January 2000 through December 2014. Results During our 15‐year study, 636 patients underwent pancreatic FNA/CNB, including 252 (40%) computerized tomography (CT) and 384 (60%) EUS‐guided biopsies. Malignancy was diagnosed in 221 (35%). Only 16 had metastases to the pancreas, comprising 2.5% of pancreatic biopsies and 7.2% of malignancies. Three (18.8%) presented with their first manifestation of cancer. EUS guidance was utilized in 50%, with rapid on‐site evaluation (ROSE) employed in 14 (88%). The most common primary site was lung (6,38%), followed by 3 (19%) each of renal and gastrointestinal malignancies. The remaining included malignant melanoma, Merkel and gallbladder small cell carcinomas, and olfactory neuroblastoma. Conclusion Cytologic diagnosis of metastasis to the pancreas is rare in our institution, comprising only 2.5% and 7.2% of total and malignant pancreatic FNA/CNB, respectively. FNA/CNB with ROSE proved to be an effective diagnostic modality, thereby obviating the need for more invasive procedures in the setting of pancreatic metastases. EUS‐FNA was equally effective as CT‐guided biopsies in achieving specimen adequacy and definitive diagnoses. We also present the first known case of a metastatic olfactory neuroblastoma to the pancreas diagnosed by imprint cytology.

With the aim to identify new second-hit mutations that cause pancreatic ductal adenocarcinoma (PDAC), other than mutations in p53, we performed a genetic interaction analysis based on the concept of mutually exclusive mutations, which suggests that mutations that are exclusive to one another function within the same pathway. Using our unbiased quantitative methods to evaluate the effects of somatic mutations on cancer we analyzed >3000 PDAC cases to prioritize mutations among hundreds that appear at low frequencies (5-10%) and that are mutually exclusive with mutations in p53. We found that mutations in RNA splicing factors SF3B1 and RBM10 (~15% of cases), were among the most significant, and mutually exclusive, to mutant p53. Thus, we hypothesized that aberrant RNA splicing promoted by SF3B1K700E and loss of RBM10 cause an oncogenic program that leads to tumorigenesis and therapy resistance. To test this hypothesis, first, we engineered mouse models to co-express KrasG12D with either Sf3b1K700E or loss of Rbm10 in Mist1 and Pdx1 driven expressing pancreatic cells. Interestingly, mice harboring KrasG12D and Sf3b1 K700E or loss of RBM10—like mutant p53—caused PDACs in mice. To identify the RNA splicing mechanism that leads to PDAC formation, we performed deep RNA sequencing and unbiased transcriptome-wide splicing analyses in isolated PDAC cells bearing wild-type, SF3B1K700E and loss of RBM10, derived from murine and patient PDACs. We found that like the splicing defects induced by p53mut—SF3B1K700E or loss of RBM10—induce splicing defects in sequence-specific coding exons in mRNAs derived from chromosomes 19, 7, 1 and 2 and impacting mainly GTPase activation and lipid metabolism pathways across species models. Consistent with this common mechanism, we found that PDAC cells do not tolerate the forced expression of mutant p53 with either SF3B1K700E or loss of Rbm10, supporting the mutual exclusivity findings from patient samples. To determine a personalized therapy pathway for patients bearing mutant splicing-factor tumors, we found that PDAC cells with SF3B1K700E or RBM10 loss cells are more sensitive to Gemcitabine rather than 5FU, which are the two main chemotherapeutic components of the two standard-of-care therapies. In addition, these mutations sensitize cells to small-molecule splicing inhibitor H3B-8800, which has advanced to phase 2 trial for hematologic malignancies. Lastly, we found that combination of Gemcitabine and H3B-8800 synergize to selective kill mutant splicing cells. We are currently testing these combination therapies in our genetically engineered mouse models and patient derived organoids. We are starting a phase 2 trial for Gemcitabine/Abraxane with escalating doses of H3B-8800 for tumors that have either SF3B1K700E, RBM10 loss or neomorphic p53, all which have aberrant RNA splicing. This work has determined novel drivers and mechanisms of PDAC development and a precision therapeutic strategy for the treatment of 45% pancreatic cancer patients (SF3B1K700E [5%], RBM10 loss [10%] and neomorphic p53 [30%]). Citation Format: Natasha Pinto Medici, Diana Martinez Saucedo, Danny Lee, Li-Ting Ku, Robert Tseng, Vincent Cannataro, Deanne Yugawa, Sumedha Chowdhury, Jeffrey Townsend, Christine A. Iacobuzio-Donahue, Omar Abdel-Wahab, Steven D. Leach, Luisa Escobar-Hoyos. Altered RNA splicing causes pancreatic cancer and exposes a therapeutic vulnerability [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr A055.