Serendipity Strikes: How Pursuing Novel Hypotheses Shifted the Paradigm Regarding the Genetic Basis of Colorectal Cancer and Changed Cancer Therapy.

In this installment of the "Paradigm Shifts in Perspective" series, the authors, all scientists who have been involved in colorectal cancer (CRC) research for most or all of their careers, have watched the field develop from early pathological descriptions of tumor formation to the current understanding of tumor pathogenesis that informs personalized therapies. We outline how our understanding of the pathogenetic basis of CRC began with seemingly isolated discoveries-initially with the mutations in RAS and the APC gene, the latter of which was initially found in the context of intestinal polyposis, to the more complex process of multistep carcinogenesis, to the chase for tumor suppressor genes, which led to the unexpected discovery of microsatellite instability (MSI). These discoveries enabled the authors to better understand how the DNA mismatch repair (MMR) system not only recognizes DNA damage but also responds to damage by DNA repair or by triggering apoptosis in the injured cell. This work served, in part, to link the earlier findings on the pathogenesis of CRC to the development of immune checkpoint inhibitors, which has been transformative-and curative-for certain types of CRCs and other cancers as well. These discoveries also highlight the circuitous routes that scientific progress takes, which can include thoughtful hypothesis testing and at other times recognizing the importance of seemingly serendipitous observations that substantially change the flow and direction of the discovery process. What has happened over the past 37 years was not predictable when this journey began, but it does speak to the power of careful scientific experimentation, following the facts, perseverance in the face of opposition, and the willingness to think outside of established paradigms.

Stem Cell Theory of Cancer: Origin of Metastasis and Sub-clonality.

Metastasis may be the secret weapon cancer uses to dominate and subjugate, to persist and prevail. However, it is no longer a secret when we realize that a stem cell has the same ways and means to fulfill its own omnipotence and accomplish its own omnipresence… and when we realize that a cancer cell has its own version of stem-ness origin and stem-like nature. In this perspective, we discuss whether stem-ness enables metastasis or mutations drive metastasis. We ponder about low-grade versus high-grade tumors and about primary versus metastatic tumors. We wonder about stochasticity and hierarchy in the genesis and evolution of cancer and of metastasis. We postulate that metastasis may hold the elusive code that makes or breaks a stem-cell versus a genetic theory of cancer. We speculate that the vaunted model of multistep carcinogenesis may be in error and needs some belated remodeling and a major overhaul. We propose that subsequent malignant neoplasms from germ cell tumors and donor-derived malignancies in organ transplants are quintessential experiments of nature and by man that may eventually empower us to elucidate a stem-cell origin of cancer and metastasis. Unfortunately, even the best experiments of cancer and of metastasis will be left unfinished, overlooked, or forgotten, when we do not formulate a proper cancer theory derived from pertinent and illuminating clinical observations. Ultimately, there should be no consternations when we realize that metastasis has a stem-cell rather than a genetic origin, and no reservations when we recognize that metastasis has been providing us some of the most enduring tests and endearing proofs to demonstrate that cancer is indeed a stem-cell rather than a genetic disease after all.

Determining cancer risk: the evolutionary multistage model or total stem cell divisions?

A recent hypothesis proposed that the total number of stem cell divisions in a tissue (TSCD model) determine its intrinsic cancer risk; however, a different model-the multistage model-has long been used to understand how cancer originates. Identifying the correct model has important implications for interpreting the frequency of cancers. Using worldwide cancer incidence data, we applied three tests to the TSCD model and an evolutionary multistage model of carcinogenesis (EMMC), a model in which cancer suppression is recognized as an evolving trait, with natural selection acting to suppress cancers causing a significant mean loss of Darwinian fitness. Each test supported the EMMC but contradicted the TSCD model. This outcome undermines results based on the TSCD model quantifying the relative importance of 'bad luck' (the random accumulation of somatic mutations) versus environmental and genetic factors in determining cancer incidence. Our testing supported the EMMC prediction that cancers of large rapidly dividing tissues predominate late in life. Another important prediction is that an indicator of recent oncogenic environmental change is an unusually high mean fitness loss due to cancer, rather than a high lifetime incidence. The evolutionary model also predicts that large and/or long-lived animals have evolved mechanisms of cancer suppression that may be of value in preventing or controlling human cancers.

Cancer-related genetic changes in multistep hepatocarcinogenesis and their correlation with imaging and histological findings.

AIM: The landscape of cancer-related genetic aberrations in hepatocellular carcinoma (HCC) has gradually become clear through recent next-generation sequencing studies. However, it remains unclear how genetic aberrations correlate with imaging and histological findings. METHODS: Using 117 formalin-fixed paraffin-embedded specimens of primary liver tumors, we undertook targeted next-generation sequencing of 50 cancer-related genes and digital polymerase chain reaction of hTERT. After classifying tumors into several imaging groups by hierarchal clustering with the information from gadoxetic acid enhanced magnetic resonance imaging, contrast-enhanced computed tomography, contrast-enhanced ultrasound, and diffusion-weighted imaging magnetic resonance imaging, the correlation between genetic aberrations and imaging and histology were investigated. RESULTS: Most frequent mutations were hTERT (61.5%), followed by TP53 (42.7%), RB1 (24.8%), and CTNNB1 (18.8%). Liver tumors were classified into six imaging groups/grades, and the prevalence of hTERT mutations tended to increase with the advancement of imaging/histological grades (P = 0.026 and 0.13, respectively), whereas no such tendency was evident for TP53 mutation (P = 0.78 and 1.00, respectively). Focusing on the mutations in each tumor, although the variant frequency (VF) of hTERT did not change (P = 0.36 and 0.14, respectively) in association with imaging/histological grades, TP53 VF increased significantly (P = 0.004 and <0.001, respectively). In multivariate analysis, stage III or IV (hazard ratio, 3.64; P = 0.003), TP53 VF ≥ 50% (hazard ratio, 3.79; P = 0.020) was extracted as an independent risk for recurrence in primary HCC patients. CONCLUSIONS: Increased prevalence of hTERT mutation and increased TP53 mutation VF are characteristic features of HCC progression, diagnosed with imaging/histological studies.

Deciphering nasopharyngeal carcinoma pathogenesis via proteomics.

Introduction: Nasopharyngeal carcinoma (NPC) is a distinct head and neck squamous cell carcinoma in its etiological association of Epstein-Barr virus (EBV) infection, hidden anatomical location, remarkable racial and geographical distribution, and high incidence of locoregional recurrence or metastasis. Thanks to the advancements in proteomics in recent decades, more understanding of the disease etiology, carcinogenesis, and progression has been gained, potentially deciphering the molecular characteristics of the malignancy. Areas covered: In this review, we provide an overview of the proteomic aberrations that are likely involved or drive NPC development and progression, focusing on the contributions of major EBV-encoded factors, intercommunication with environment, protein features of high metastasis and therapy resistance, and protein-protein interactions that allow NPC cells to evade immune recognition and elimination. Finally, multistep carcinogenesis and subtypes of NPC from a proteomic perspective are inquired. Expert commentary: Proteomic studies have covered various aspects involved in NPC pathogenesis, yet much remains to be uncovered. Coherent study designs, optimal conditions for obtaining high-quality data, and compelling interpretation are critical in ensuring the emergence of good science out of NPC proteomics. NPC proteogenomics and proteoform analysis are two promising fields to promote the application of the proteomic findings from bench to bedside.

A new era for understanding genetic evolution of multistep carcinogenesis.

Cancer development is a multistep process involving genetic and cellular alterations, and recent advances in next-generation sequencing have elucidated mutation landscapes of premalignant lesions as well as early- and late-stage tumors. In this issue of Journal of Gastroenterology, Kim and colleagues contributed to the better understanding of genetic events in putative precursors of hepatocellular carcinoma (HCC). Precancerous tissues are divided into canonical and non-canonical types, which share common driver mutations with cancerous lesions or not, and potential gatekeeper gene(s) for clonal selection play a critical role in driving precursors to cancers not only in HCC, but also in esophageal, gastric, colorectal, and pancreatic cancers.

Bases evolutivas y ecológicas de la carcinogénesis humana ¿cuestión de mala suerte? / Evolutionary and ecological bases of human carcinogenesis, a matter of bad luck?

El cáncer constituye un serio problema de salud a nivel mundial. Las estimaciones, en cuanto a incidencia y mortalidad, no son nada halagüeñas, en especial para los países subdesarrollados. Durante las últimas décadas se han realizado importantes contribuciones a la comprensión de la carcinogénesis humana, sobre todo desde la perspectiva ecológica y evolutiva. Los objetivos del presente trabajo se centran en: destacar las principales hipótesis que desde dicha perspectiva, tratan de explicar la etiología de los tumores malignos, así como adecuar las que, a la luz de los hallazgos recientes o cotejadas con datos empíricos, parecen más factibles. La hipótesis tradicionalmente aceptada se basa en la carcinogénesis en múltiples etapas y explica de manera satisfactoria algunos aspectos del proceso; aunque conlleva a falacias de lógica, como la conclusión que dos tercios de los cánceres humanos obedecen a la mala suerte. Por su parte, la hipótesis de la oncogénesis adaptativa parece adecuarse de manera más realística a las complejas relaciones ecológicas que se establecen entre las células malignas, las células normales y el microambiente celular; capaces de originar fenómenos tan inadmisibles, como la cooperación de células normales en la progresión tumoral o la adopción por parte de las células malignas de estrategias evolutivamente estables. De hecho, la oncogénesis adaptativa incluso puede ser extendida al nivel del macroambiente poblacional y social. Su conclusión definitiva no hace más que reiterar la importancia de la prevención como la medida más eficaz para reducir la carga global de enfermedad por cáncer(AU)

Cancer is a serious health problem worldwide. Estimates, in terms of incidence and mortality, are not at all promising especially for underdeveloped countries. During the last decades, important contributions have been made to the understanding of human carcinogenesis, especially from the ecological and evolutionary perspective. The objectives of this work are focused on: highlighting the main hypotheses that, from this perspective, try to explain the etiology of malignant tumors, as well as adapting those that, in the light of recent findings or collated with empirical data, seem more feasible. The traditionally accepted hypothesis is based on multi-stage carcinogenesis; and satisfactorily explains some aspects of the process; although it leads to logic fallacies, such as the conclusion that two thirds of human cancers obey to bad luck. On the other hand, the hypothesis of adaptive oncogenesis seems to adapt more realistically to the complex ecological relationships established between malignant cells, normal cells, and the cellular microenvironment; capable of originating such inadmissible phenomena, such as the cooperation of normal cells in tumor progression, or the adoption by malignant cells of evolutionarily stable strategies. In fact, adaptive oncogenesis can even be extended to the level of the population and social "macroenvironment". Its final conclusion does nothing but reiterate the importance of prevention as the most effective measure to reduce the global burden of cancer disease(AU)

Bases evolutivas y ecológicas de la carcinogénesis humana ¿cuestión de mala suerte? / Evolutionary and ecological bases of human carcinogenesis, a matter of bad luck?

El cáncer constituye un serio problema de salud a nivel mundial. Las estimaciones, en cuanto a incidencia y mortalidad, no son nada halagüeñas, en especial para los países subdesarrollados. Durante las últimas décadas se han realizado importantes contribuciones a la comprensión de la carcinogénesis humana, sobre todo desde la perspectiva ecológica y evolutiva. Los objetivos del presente trabajo se centran en: destacar las principales hipótesis que desde dicha perspectiva, tratan de explicar la etiología de los tumores malignos, así como adecuar las que, a la luz de los hallazgos recientes o cotejadas con datos empíricos, parecen más factibles. La hipótesis tradicionalmente aceptada se basa en la carcinogénesis en múltiples etapas y explica de manera satisfactoria algunos aspectos del proceso; aunque conlleva a falacias de lógica, como la conclusión que dos tercios de los cánceres humanos obedecen a la mala suerte. Por su parte, la hipótesis de la oncogénesis adaptativa parece adecuarse de manera más realística a las complejas relaciones ecológicas que se establecen entre las células malignas, las células normales y el microambiente celular; capaces de originar fenómenos tan inadmisibles, como la cooperación de células normales en la progresión tumoral o la adopción por parte de las células malignas de estrategias evolutivamente estables. De hecho, la oncogénesis adaptativa incluso puede ser extendida al nivel del macroambiente poblacional y social. Su conclusión definitiva no hace más que reiterar la importancia de la prevención como la medida más eficaz para reducir la carga global de enfermedad por cáncer(AU)

Cancer is a serious health problem worldwide. Estimates, in terms of incidence and mortality, are not at all promising especially for underdeveloped countries. During the last decades, important contributions have been made to the understanding of human carcinogenesis, especially from the ecological and evolutionary perspective. The objectives of this work are focused on: highlighting the main hypotheses that, from this perspective, try to explain the etiology of malignant tumors, as well as adapting those that, in the light of recent findings or collated with empirical data, seem more feasible. The traditionally accepted hypothesis is based on multi-stage carcinogenesis; and satisfactorily explains some aspects of the process; although it leads to logic fallacies, such as the conclusion that two thirds of human cancers obey to bad luck. On the other hand, the hypothesis of adaptive oncogenesis seems to adapt more realistically to the complex ecological relationships established between malignant cells, normal cells, and the cellular microenvironment; capable of originating such inadmissible phenomena, such as the cooperation of normal cells in tumor progression, or the adoption by malignant cells of evolutionarily stable strategies. In fact, adaptive oncogenesis can even be extended to the level of the population and social "macroenvironment". Its final conclusion does nothing but reiterate the importance of prevention as the most effective measure to reduce the global burden of cancer disease(AU)

The PD-1/PD-L1 axis may be aberrantly activated in occupational cholangiocarcinoma.

An outbreak of cholangiocarcinoma in a printing company was reported in Japan, and these cases were regarded as an occupational disease (occupational cholangiocarcinoma). This study examined the expression status of programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) in occupational cholangiocarcinoma. Immunostaining of PD-1, PD-L1, CD3, CD8, and CD163 was performed using tissue sections of occupational cholangiocarcinoma (n = 10), and the results were compared with those of control cases consisting of intrahepatic (n = 23) and extrahepatic (n = 45) cholangiocarcinoma. Carcinoma cells expressed PD-L1 in all cases of occupational cholangiocarcinoma, whereas the detection of PD-L1 expression in cholangiocarcinoma cells was limited to a low number of cases (less than 10%) in the control subjects. In cases of occupational cholangiocarcinoma, occasional PD-L1 expression was also noted in precancerous/preinvasive lesions such as biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct. Additionally, tumor-associated macrophages and tumor-infiltrating T cells expressed PD-L1 and PD-1, respectively. The number of PD-L1-positive mononuclear cells, PD-1-positive lymphocytes, and CD8-positive lymphocytes infiltrating within the tumor was significantly higher in occupational cholangiocarcinoma compared with that in control cases. These results indicate that immune escape via the PD-1/PD-L1 axis may be occurring in occupational cholangiocarcinoma.

Altered expression of CKs 14/20 is an early event in a rat model of multistep bladder carcinogenesis.

Cytokeratins (CKs) 14 and 20 are promising markers for diagnosing urothelial lesions and for studying their prognosis and histogenesis. This work aimed to study the immunohistochemical staining patterns of CK14/20 during multistep carcinogenesis leading to papillary bladder cancer in a rat model. Thirty female Fischer 344 rats were divided into three groups: group 1 (control); group 2, which received N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) for 20 weeks plus 1 week without treatment; and group 3, which received BBN for 20 weeks plus 8 weeks without treatment. Bladder lesions were classified histologically. CK14 and CK20 immunostaining was assessed according to its distribution and intensity. In control animals, 0-25% of basal cells and umbrella cells stained positive for CK14 and CK20 respectively. On groups 2 and 3, nodular hyperplastic lesions showed normal CK20 and moderately increased CK14 staining (26-50% of cells). Dysplasia, squamous metaplasia, papilloma, papillary tumours of low malignant potential and low- and high-grade papillary carcinomas showed increased CK14 and CK20 immunostaining in all epithelial layers. Altered CK14 and CK20 expression is an early event in urothelial carcinogenesis and is present in a wide spectrum of urothelial superficial neoplastic and preneoplastic lesions.

Transarterial chemoembolization using iodized oil for unresectable hepatocellular carcinoma: perspective from multistep hepatocarcinogenesis.

Transarterial chemoembolization (TACE) using iodized oil (Lipiodol(®)) (Lp-TACE) as a carrier of chemotherapeutic agents has been routinely performed to control hepatocellular carcinomas (HCC) in Japan, and its use has yielded fairly beneficial therapeutic results. Lipiodol is thought to pass through the tumor sinusoids of HCC and reach the outflow drainage areas, namely, the portal venous side of the tumor. By doing this, Lipiodol blocks not only the tumor's arterial inflow but also its portal venous outflow, providing sufficient ischemic effects. It is known that the inflow blood system, tumor sinusoids, and outflow blood system change drastically during the process of multistep hepatocarcinogenesis; thus, it is reasonable to postulate that the distribution of Lipiodol and the subsequent therapeutic effect of Lp-TACE may also change during that process. Arterial inflow to HCC is highest for moderately differentiated HCC (mHCC) and is relatively low in well or poorly differentiated HCC (wHCC and pHCC, respectively). It has been suggested that the metabolic state of wHCC and mHCC is aerobic, while that of pHCC is anaerobic. The tumor sinusoids in wHCC and mHCC are small in size and large in number, while those in pHCC are large in size and small in number. This finding results in a greater chance of tumor cell exposure to chemotherapeutic agents in the former and a lesser chance in the latter. The outflow tract, namely, the drainage system via the residual portal venous branches within the pseudocapsule, is more complete in mHCC and pHCC and less so in wHCC. Considering all of these components of HCC of different histological grades, Lp-TACE should have the greatest effect on mHCC and a relatively low effect on wHCC and pHCC. To achieve consistently high therapeutic results, it is important to consider these components, which affect the sensitivity of HCC to Lp-TACE, to maximize both the chemotherapeutic and ischemic effects of this therapy.

Adenoma-carcinoma Sequence in the Bladder After Augmentation Cystoplasty.

We present a case of a 64-year-old woman showing multistep progression from adenoma to adenocarcinoma in the bladder 46 years after augmentation ileocystoplasty. She underwent augmentation ileocystoplasty for tuberculous contracted bladder at 18 years. After 44 years, tubulovillous adenomas were found and resected at the ileovesical anastomosis site. After 2 more years, bladder tumors recurred and revealed adenocarcinomas. Finally, radical cystectomy was required because of frequent recurrence and tumor extensiveness. To our knowledge, this is the first case demonstrating adenoma-carcinoma sequence histopathologically in the bladder after augmentation cystoplasty, indicating multistep carcinogenesis similar to intestinal carcinogenesis.