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Purpose: RB1 mutations and loss of Rb expression represent consistent but not entirely invariable hallmarks of small cell lung cancer (SCLC). The prevalence and characteristics of SCLC retaining wild-type Rb are not well-established. Furthermore, the performance of targeted next-generation sequencing (NGS) vs immunohistochemistry for Rb assessment are not well-defined. Experimental design: 208 clinical SCLC samples were analyzed by comprehensive targeted NGS, covering all exons of RB1, and Rb immunohistochemistry. Based on established coordination of Rb/p16/cyclinD1 expression, p16-high/cyclinD1-low profile was used as marker of constitutive Rb deficiency. Results: Fourteen of 208 (6%) SCLC expressed wild-type Rb, accompanied by a unique p16-low/cyclinD1-high profile supporting Rb proficiency. Rb-proficient SCLC were associated with neuroendocrine-low phenotype, combined SCLC with non-SCLC (NSCLC) histology and aggressive behavior. These tumors exclusively harbored CCND1 amplifications (29%), and were markedly enriched in CDKN2A mutations (50%) and NSCLC-type alterations (KEAP1, STK11, FGFR1). The remaining 194/208 SCLC were Rb-deficient (p16-high/cyclinD1-low), including 184 cases with Rb loss (of which 29% lacked detectable RB1 alterations by clinical NGS pipeline), and 10 cases with mutated but expressed Rb. Conclusion: This is the largest study to-date to concurrently analyze Rb by NGS and immunohistochemistry in SCLC, identifying a 6% rate of Rb proficiency. Pathologic-genomic data implicate NSCLC-related progenitors as a putative source of Rb-proficient SCLC. Consistent upstream Rb inactivation via CDKN2A/p16↓ and CCND1/cyclinD1↑ suggests potential utility of CDK4/6 inhibitors in this aggressive SCLC subset. The study also clarifies technical aspects of Rb status determination in clinical practice, highlighting the limitations of exon-only sequencing for RB1 interrogation.

Background and Aims: Drug-induced liver injury with autoimmune features (AI-DILI) mimics the clinical presentation, and laboratory and pathologic features of idiopathic autoimmune hepatitis (AIH). We aimed to identify histopathologic hallmarks to differentiate these entities. Methods: All liver biopsies archived for the past 10 years were reviewed retrospectively to identify cases of recently detected liver injury associated with predominantly lymphoplasmacytic interphase hepatitis, positive markers for liver autoimmunity, and negative tests for viral hepatitis. Twenty cases were divided into AIH ( n = 12) or AI-DILI ( n = 8) groups. Blind qualitative evaluation of necroinflammatory changes and liver fibrosis were performed according to the Scheuer scoring system. Cellular densities were determined using ImageJ (V1.51t, National Institutes of Health, Bethesda, MD, USA). Fibrosis was assessed on Masson trichrome-stained slides, and collagen deposition was estimated following a protocol of color deconvolution. Results: Necroinflammatory changes as well as densities (portal and lobular) of neutrophils and eosinophils, intracellular cholestasis, and regenerative changes did not differ between the two groups ( P ≥ 0.05). Neutrophil densities but not eosinophils showed a positive correlation with the severity of hepatocellular damage ( r = 0.6 and 0.58, vs. alanine aminotransferase, P < 0.05). Ceroid-laden macrophages but not histiocytic aggregates appeared to be more common in AI-DILI ( P < 0.05). AIH patients presented more often with evidence of chronic damage, including higher scores of fibrosis and collagen deposition, in comparison to AI-DILI ( P < 0.05). Conclusions: Although there is no histologic feature pathognomonic for AI-DILI or AIH, advanced stages of liver fibrosis can be used to support the diagnosis of AIH in some cases. Definitive diagnosis of AI-DILI requires follow-up and demonstration of complete remission after drug withdrawal with no need for immunosuppression.

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Pancreatic ductular epithelial cells comprise the majority of duct cells in pancreas, control cystic fibrosis transmembrane conductance regulator (CFTR)-dependent bicarbonate ([Formula: see text]) secretion, but are difficult to grow as a polarized monolayer. Using NIH-3T3-J2 fibroblast feeder cells and a Rho-associated kinase inhibitor, we produced well-differentiated and polarized porcine pancreatic ductular epithelial cells. Cells grown on semipermeable filters at the air-liquid interface developed typical epithelial cell morphology and stable transepithelial resistance and expressed epithelial cell markers (zona occludens-1 and β-catenin), duct cell markers (SOX-9 and CFTR), but no acinar (amylase) or islet cell (chromogranin) markers. Polarized cells were studied in Ussing chambers bathed in Krebs-Ringer [Formula: see text] solution at 37°C gassed with 5% CO to measure short-circuit currents ( I). Ratiometric measurement of extracellular pH was performed with fluorescent SNARF-conjugated dextran at 5% CO. Cells demonstrated a baseline I (12.2 ± 3.2 μA/cm) that increased significantly in response to apical forskolin-IBMX (∆ I: 35.4 ± 3.8 μA/cm, P < 0.001) or basolateral secretin (∆ I: 31.4 ± 2.5 μA/cm, P < 0.001), both of which increase cellular levels of cAMP. Subsequent addition of apical GlyH-101, a CFTR inhibitor, decreased the current (∆ I: 20.4 ± 3.8 μA/cm, P < 0.01). Extracellular pH and [Formula: see text] concentration increased significantly after forskolin-IBMX (pH: 7.18 ± 0.23 vs. 7.53 ± 0.19; [Formula: see text] concentration, 14.5 ± 5.9 vs. 31.8 ± 13.4 mM; P < 0.05 for both). We demonstrate the development of a polarized pancreatic ductular epithelial cell epithelium with CFTR-dependent [Formula: see text] secretion in response to secretin and cAMP. This model is highly relevant, as porcine pancreas physiology is very similar to humans and pancreatic damage in the cystic fibrosis pig model recapitulates that of humans. NEW & NOTEWORTHY Pancreas ductular epithelial cells control cystic fibrosis transmembrane conductance regulator (CFTR)-dependent bicarbonate secretion. Their function is critical because when CFTR is deficient in cystic fibrosis bicarbonate secretion is lost and the pancreas is damaged. Mechanisms that control pancreatic bicarbonate secretion are incompletely understood. We generated well-differentiated and polarized porcine pancreatic ductular epithelial cells and demonstrated feasibility of bicarbonate secretion. This novel method will advance our understanding of pancreas physiology and mechanisms of bicarbonate secretion.