Most cancers in humans are large, measuring centimetres in diameter, and composed of many billions of cells1. An equivalent mass of normal cells would be highly heterogeneous as a result of the mutations that occur during each cell division. What is remarkable about cancers is that virtually every neoplastic cell within a large tumour often contains the same core set of genetic alterations, with heterogeneity confined to mutations that emerge late during tumour growth2–5. How such alterations expand within the spatially constrained three-dimensional architecture of a tumour, and come to dominate a large, pre-existing lesion, has been unclear. Here we describe a model for tumour evolution that shows how short-range dispersal and cell turnover can account for rapid cell mixing inside the tumour. We show that even a small selective advantage of a single cell within a large tumour allows the descendants of that cell to replace the precursor mass in a clinically relevant time frame. We also demonstrate that the same mechanisms can be responsible for the rapid onset of resistance to chemotherapy. Our model not only provides insights into spatial and temporal aspects of tumour growth, but also suggests that targeting short-range cellular migratory activity could have marked effects on tumour growth rates.

Background & Aims The management of pancreatic cysts poses challenges to both patients and their physicians. We investigated whether a combination of molecular markers and clinical information could improve the classification of pancreatic cysts and management of patients. Methods We performed a multi-center, retrospective study of 130 patients with resected pancreatic cystic neoplasms (12 serous cystadenomas, 10 solid-pseudopapillary neoplasms, 12 mucinous cystic neoplasms, and 96 intraductal papillary mucinous neoplasms). Cyst fluid was analyzed to identify subtle mutations in genes known to be mutated in pancreatic cysts (BRAF, CDKN2A, CTNNB1, GNAS, KRAS, NRAS, PIK3CA, RNF43, SMAD4, TP53 and VHL); to identify loss of heterozygozity at CDKN2A, RNF43, SMAD4, TP53, and VHL tumor suppressor loci; and to identify aneuploidy. The analyses were performed using specialized technologies for implementing and interpreting massively parallel sequencing data acquisition. An algorithm was used to select markers that could classify cyst type and grade. The accuracy of the molecular markers were compared with that of clinical markers, and a combination of molecular and clinical markers. Results We identified molecular markers and clinical features that classified cyst type with 90%–100% sensitivity and 92%–98% specificity. The molecular marker panel correctly identified 67 of the 74 patients who did not require surgery, and could therefore reduce the number of unnecessary operations by 91%. Conclusions We identified a panel of molecular markers and clinical features that show promise for the accurate classification of cystic neoplasms of the pancreas and identification of cysts that require surgery.

BACKGROUND & AIMS A long duration of inflammatory bowel disease (IBD) increases the risk for colorectal cancer (CRC). Mutation analysis of limited numbers of genes has indicated that colorectal tumors that develop in patients with IBD differ from those of patients without IBD. We performed whole-exome sequencing analyses to characterize the genetic landscape of these tumors. METHODS We collected colorectal tumor and non-neoplastic tissues from 31 patients with IBD and CRC (15 with ulcerative colitis, 14 with Crohn’s disease, and 2 with indeterminate colitis) and performed whole-exome sequencing analyses of the micro-dissected tumor and matched non-tumor tissues. We identified somatic alterations by comparing matched specimens. The prevalence of mutations in sporadic colorectal tumors was obtained from previously published exome-sequencing studies. RESULTS Two specimens had somatic mutations in the DNA-proofreading or mismatch repair genes POLE, MLH1, and MSH6 and the tumor cells had a hypermutable phenotype. The remaining tumors had, on average, 71 alterations per sample. TP53 was the most commonly mutated gene, with and incidence prevalence similar to that of sporadic colorectal tumors (63% of cases). However, tumors from the patients with IBD had a different mutation spectrum. APC and KRAS were mutated at significantly lower rates in tumors from patients with IBD than in sporadic colorectal tumors (13% and 20% of cases, respectively). Several genes were mutated more frequently or uniquely in tumors from patients with IBD, including SOX9 and EP300 (which encode proteins in the WNT pathway), NRG1 (which encodes an ERBB ligand), and IL16 (which encodes a cytokine). Our study also revealed recurrent mutations in components of the Rho and Rac GTPase network, indicating a role for non-canonical WNT signaling in development of colorectal tumors in patients with IBD. CONCLUSIONS Colorectal tumors that develop in patients with IBD have distinct genetic features from sporadic colorectal tumors. These findings could be used to develop disease-specific markers for diagnosis and treatment of patients with IBD and CRC.

High-grade pancreatic intraepithelial neoplasia (HG-PanIN) is the major precursor of pancreatic ductal adenocarcinoma (PDAC) and is an ideal target for early detection. To characterize pure HG-PanIN, we analysed 23 isolated HG-PanIN lesions occurring in the absence of PDAC. Whole-exome sequencing of five of these HG-PanIN lesions revealed a median of 33 somatic mutations per lesion, with a total of 318 mutated genes. Targeted next-generation sequencing of 17 HG-PanIN lesions identified KRAS mutations in 94% of the lesions. CDKN2A alterations occurred in six HG-PanIN lesions, and RNF43 alterations in five. Mutations in TP53, GNAS, ARID1A, PIK3CA, and TGFBR2 were limited to one or two HG-PanINs. No non-synonymous mutations in SMAD4 were detected. Immunohistochemistry for p53 and SMAD4 proteins in 18 HG-PanINs confirmed the paucity of alterations in these genes, with aberrant p53 labelling noted only in three lesions, two of which were found to be wild type in sequencing analyses. Sixteen adjacent LG-PanIN lesions from ten patients were also sequenced using targeted sequencing. LG-PanIN harboured KRAS mutations in 94% of the lesions; mutations in CDKN2A, TP53, and SMAD4 were not identified. These results suggest that inactivation of TP53 and SMAD4 are late genetic alterations, predominantly occurring in invasive PDAC.

A new evaluation of previously published data suggested to us that the accumulation of mutations might slow, rather than increase, as individuals age. To explain this unexpected finding, we hypothesized that normal stem cell division rates might decrease as we age. To test this hypothesis, we evaluated cell division rates in the epithelium of human colonic, duodenal, esophageal, and posterior ethmoid sinonasal tissues. In all 4 tissues, there was a significant decrease in cell division rates with age. In contrast, cell division rates did not decrease in the colon of aged mice, and only small decreases were observed in their small intestine or esophagus. These results have important implications for understanding the relationship between normal stem cells, aging, and cancer. Moreover, they provide a plausible explanation for the enigmatic age-dependent deceleration in cancer incidence in very old humans but not in mice.

- Our understanding of the molecular alterations that lead from pancreatic precursor lesion to invasive carcinoma continues to evolve. These advances aid clinicians in their treatment decisions and researchers in their search for actionable, druggable targets.

Background The Liver Imaging Reporting and Data System (LI‐RADS) is being adapted by many clinical practices. To support continuation of its use, LI‐RADS (LR) is in need of multicenter validation studies of recent LI‐RADS iterations. Furthermore, while both gadoxetate and extracellular agents have been incorporated into LI‐RADS, comparison of the diagnostic performance between the two has yet to be determined. Purpose/Hypothesis To evaluate the rate, diagnostic performance, and interreader reliability (IRR) of LI‐RADS 2017 for hepatocellular carcinoma, including LR major and ancillary features, with both gadoxetate and extracellular agent‐enhanced MRI against a reference standard of histopathology or imaging follow‐up. Study Type Retrospective. Population In all, 114 patients with 144 observations were included who met LR 2017 criteria for at risk and had at least one hepatic observation on liver MRI performed with either gadoxetate (n = 52) or an extracellular agent (n = 92) between 2010–2016, with histopathology (n = 103) or follow‐up imaging (n = 41). Field Strength/Sequence 1.5 and 3.0T/T1‐T2WI, diffusion‐weighted imaging. Assessment Three radiologists independently assessed major/ancillary features and assigned overall LI‐RADS category for every observation. Statistical Tests Diagnostic performance of LR5/TIV+LR5 for identifying hepatocellular carcinoma (HCC) was compared between contrast agents with a generalized estimating equation. Weighted kappa was performed for interrater reliability. Results The frequency of HCCs among LR1, LR2, LR3, L4, LR5, LRTIV+LR5, and LRM observations were: 0% (all readers), 0–12.5%, 11.4–26.9%, 50–76%, 83.0–95.1%, 83.3–100.0%, and 45.0–65.0%, respectively. Sensitivity of LR5/LRTIV+LR5 for HCC was 59.7–71.4% and specificity 85.0–96.8%. LI‐RADS specificity and positive predictive value for observations imaged with gadoxetate was higher than extracellular agent for the most inexperienced reader (R3) (P = 0.009–0.034). IRR for LI‐RADS categorization was substantial (k = 0.661). Data Conclusion Increasing numerical LI‐RADS 2017 categories demonstrate a greater percentage of HCCs. LR5/TIV+LR5 demonstrates excellent specificity and fair sensitivity for HCC. MRI with gadoxetate in liver transplant candidates may be beneficial for less experienced readers, although further large‐scale prospective studies are needed. Level of Evidence: 4 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019;49:e205–e215.

Context.-Experiences at our institution show that flow cytometry analysis (FCA) has become routine clinical practice in the workup of patients with altered mental status, even if risk factors are low.Objective.-To assess diagnostic accuracy of combined FCA and cytology in the diagnosis of central nervous system lymphoma in an unselected patient population with neurologic symptoms, including patients with no history of lymphoma or suspicious radiology.Design.-Between 2001 and 2011, cerebrospinal fluid was submitted from 373 patients for lymphoma screening by FCA. The medical records were reviewed for patient symptomatology, history of malignancy, brain imaging, FCA results, cytology results, brain biopsy, and clinical follow-up.Results.-A lymphoid malignancy was detected by FCA in 4% of cases. A positive diagnosis was more likely in patients with either a history of hematologic malignancy and/or a suspicious radiology result (P ¼ .009). All patients with no history of lymphoma and no suspicious radiology (n ¼ 102) had negative cytology, and none had a correspondingly positive FCA result. The positive and negative predictive values of combined cytology and FCA in the patients with history of lymphoma and/or abnormal imaging results were 92% and 89%, respectively, when compared with open brain tissue biopsy, and 89% and 86%, respectively, when compared with clinical followup. When low-risk patients were included, the positive predictive value remained at 92%, but the negative predictive value dropped to 52% with the open brain biopsy as the reference, and values did not change significantly for the group with clinical follow-up.Conclusions.-Concurrent FCA and cytology are most useful in the appropriate clinical setting, and we propose a triage algorithm for how FCA on cerebrospinal fluid is best used.