BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies. Its larger mass size is widely acknowledged to be associated with increased lymph node (LN) metastatic potential. However, the quantitative relationships between tumor size and LN metastasis or survival remain unclear. Thus, this study aims to quantitatively identify the objective relationship between tumor size and prevalence of LN metastases across primary tumor size spectrums. METHODS: 9,958 resected PDAC patients without distant metastasis were retrieved from the Surveillance, Epidemiology, and End Results (SEER) database. The prevalence of LN metastases, LN ratio (LNR) and N2/N1 ratio were assessed amongst different tumor sizes, and the relationships were depicted by matched curves.RESULTS: In the enrolled cohort, age, tumor site, grade, American Joint Committee on Cancer (AJCC) 8th node staging, tumor size, chemotherapy and radiotherapy were identi ed as signi cant independent predictors for overall survival (OS) and cancer-speci c survival (CSS). For tumors within 1-40 mm in size, the prevalence of node positive disease is closely modelled using a logarithmic formula [0.249×ln (size) + 0.452] × 100%, and then uctuated between 70.0% and 80.0% when beyond 40 mm. The mean LNR increased in a stepwise manner as tumor size increased from 1-5 mm (LNR=0.024) to 41-45 mm (LNR=0.177); then, beyond 45 mm, it plateaued near 0.170. N2/N1 ratio gradually increased along with tumor size from 1-5 mm (N2/N1=0.286) to 41-45 mm (N2/N1=1.016), and when tumor size reached to 41-45 mm or more, the ratio stabilized around 1.000. CONCLUSION: Regional LN involvement demonstrated a logarithmic growth with increasing tumor sizes in resectable PDAC patients. The probability of metastasis in each regional LN for resectable PDAC patients with tumors greater than 40 mm in size was near 17.0% and their overall prevalence of LN metastasis was 70%-80%. Among which, 50% of patients had an N2 stage.

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CD4+ T-cell-converted CD4−CD8− double negative (cDNT) have strong suppressive activity in the maintenance of immune tolerance, whereas IL-2 promotes cDNT proliferation and enhances cDNT resistance to apoptosis. However, the intrinsic mechanisms that regulate the survival of cDNT are still unknown. Here we demonstrate that the OX40 molecule was highly expressed on cDNT. The expression of OX40 was necessary to promote proliferation and inhibit apoptosis of cDNT in vivo and in vitro. OX40 promoted the survival of cDNT by regulating the expression of Bcl-2, Bcl-xL, Survivin, and BCL2L11. Canonical NF-κB cell signaling played an important role in the transmission of essential division and survival signals through OX40 in cDNT. IL-2 promoted the survival of cDNT in part via elevating the expression of the OX40 molecule. IL-2 promoted OX40 expression via downregulating the PPARα expression. In conclusion, we elucidated that OX40 is a key molecule that regulates cDNT proliferation and survival. IL-2 promoted OX40 expression by downregulating the PPARα binding to the OX40 promoter, leading to the elevated expression of Bcl-2, Bcl-xL, and Survivin in cDNT, which finally resulted in the promoted proliferation and decreased apoptosis of cDNT.