Chemoprevention: What Researchers Are Learning From Your Mom

By: Martin Smith, as a member of RIOT

chemoprevention blog

Your Mom would be very happy.  Cancer researchers have published studies showing that eating vegetables like broccoli may lower the risk for developing some cancers (1). Taking this idea one step further, researchers want to know if we can extract a key compound from vegetables and put it into pill form.  But, can a pill really replace eating your daily dose of broccoli?  These are the questions that cancer researchers are trying to answer right now.  A compound found in cruciferous vegetables called sulforaphane has been identified as a possible chemoprevention treatment against cancer.

Chemoprevention is not like standard chemotherapy.  This experimental treatment option is aimed at preventing the onset of cancer by providing a daily therapy to people who may be at higher risks of developing a disease.   Much like a vitamin, the power of chemoprevention is through ongoing treatment to lower the risks of getting cancer.  Potential chemoprevention drugs, like sulforaphane, are absorbed by the body and prevent the formation of cancer-causing agents in the body. They also increase the body’s machinery to clean up carcinogens out of the system before they damage cells.  We are still learning a lot about the possibility of using chemoprevention and researchers are conducting new studies to determine exactly what this means.

In one study, a protein called tubulin was identified as a target for chemoprevention treatment using sulforaphane (2).  Tubulin is the skeleton of your cells and when cancer grows it often takes advantage of changes in the shape of your cells. Researchers are hoping that sulforaphane prevents tubulin malfunction and restores healthy function.  In another example, studies suggest that sulforaphane, along with other dietary compounds, may prevent cancer by turning “on” or “off” a gene connected to both cell growth and clean up.  Giving prostate cancer cells sulforaphane led to slower cancer growth by turning off the genes (3).  As exciting as these studies are, they do not explain how sulforaphane can create longstanding effects on our body.  Understandably, scientists need to go deeper to understand the underlying causes before considering this as a mainstream therapy.

Since before Watson and Crick, we have known that all of the information needed to create life is found within our genes – our genetic code.  Unlocking our genetic code has helped us to understand what it means to be human.  Now researchers are starting to appreciate that in addition to our genetic code, there are important ways to regulate how we read the code. One such process of regulation is known as epigenetics and it is having a profound effect on how we treat cancer.  As researchers learn more about epigenetics they will undoubtedly identify other compounds like sulforaphane, that prevent cancer by changing how we read our DNA.

So what do we do while researchers figure out how to harness the potential of sulforaphane?

For now the answer is found in the advice you were probably given as a child.  Eat your broccoli!  Organizations like the Canadian Cancer Society have worked closely with dieticians to show the importance of a balanced diet. Including preventing cancer.  One diet plan can be found here:

http://www.cancer.ca/en/prevention-and-screening/live-well/nutrition-and-fitness/eating-well/?region=on

This article was written by Dr. Martin Smith. Dr. Smith completed his PhD at the University of Waterloo studying how proteins can cause cancer. He currently works for the Ontario Brain Institute where he studies brain disease. To learn more about Dr. Smith and his research check out our members page.

References:

(1) Dosz EB, Jeffery EH. Modifying the processing and handling of frozen broccoli for increased sulforaphane formation. J Food Sci., Volume 78(9), September 2013,  Pages 1459-63

(2) Xiao Z, Mi L, Chung FL, Veenstra TD. Proteomic analysis of covalent modifications of tubulins by isothiocyanates. J Nutr., Volume 142(7), July 2012,  Pages 1377-81.

(3) Beaver, LM., et al. Long noncoding RNAs and sulforaphane: a target for chemoprevention and suppression of prostate cancer. The Journal of Nutritional Biochemistry, Volume 42, April 2017, Pages 72-83

Awakening Cancer-Fighting Cells of the Immune System Using Radiation Therapy

By: Joseph Longo

T Cell

About half of all cancer patients will be treated with radiation therapy at some point during the course of their disease. Conventional radiation therapy involves the delivery of high doses of radiation to the tumour, usually in multiple smaller doses called fractions. When a cell is irradiated, its DNA becomes damaged. If this damage is left unrepaired, the cell dies. Unlike chemotherapy, which is usually delivered throughout the entire body, radiation therapy is delivered with high precision to a specific area. As a result, DNA damage only occurs in those cells within the radiation field. However, oncologists have noticed that, in a small number of patients with multiple tumours in different locations within the body, the delivery of radiation to one tumour can cause the other tumours outside of the radiation field to shrink in size.

How is this possible? The answer seems to lie within the immune system. When cancer cells die in response to radiation therapy, they release proteins and other molecules into the surrounding environment. These molecules act as “danger signals” that alert and recruit cells from the patient’s immune system. Immune cells known as T cells can recognize certain cancer-specific proteins as “foreign material”, which results in their activation. These activated T cells can then circulate the body and kill any cancer cell that displays that same foreign protein.

What does this mean for a patient receiving radiation therapy? Not only can radiation therapy directly kill cancer cells by causing DNA damage, but, in certain cases, it can also activate and exploit the patient’s immune system to kill cancer cells that may have survived the radiation treatment or spread to other parts of the body. This phenomenon is commonly referred to as the abscopal effect, and has been reported in several different cancer types, including lymphoma, melanoma and hepatocellular carcinoma [1].

In some cancers, the expression of certain proteins on the surface of the cancer cell can mask them from the immune system. Many of these proteins are now the targets for a class of cancer immunotherapy drugs called immune checkpoint inhibitors. The inhibitors work by blocking these cell surface proteins so that T cells can attack and kill the cancer cells. While these immune checkpoint inhibitors have resulted in some dramatic responses in a subset of cancer patients, the number of patients who benefit from immune checkpoint therapies is low [2]. Many clinical trials are now investigating the potential for radiation therapy to increase the number of patients who can benefit from immune checkpoint therapies in a number of different cancer types [3]. In a recent case report, a melanoma patient who progressed while on an immune checkpoint inhibitor, called ipilimumab, was subsequently prescribed palliative radiation therapy and an additional dose of ipilimumab. Remarkably, not only did the patient’s irradiated tumour shrink, but so did the tumours outside of the radiation field [4].

While promising, it should be noted that the abscopal effect of radiation therapy is a rare phenomenon, and more research is needed to fully understand the mechanism by which it occurs and how best to exploit it. In recent pre-clinical studies, it was identified that repeated low doses of radiation in combination with immune checkpoint inhibitors was more effective at activating tumour-specific T cells and inhibiting tumour growth compared to single, higher doses of radiation [5-6]. These studies have important clinical implications, as they suggest that certain radiation doses and fractionation schedules may be more effective at eliciting the abscopal effect than others. The results of on-going clinical trials and further basic research will inform us how best to use radiation therapy in combination with cancer immunotherapies going forward, and have the potential to greatly influence cancer patient care.

This article was written by Joseph Longo. Joseph is currently pursuing a PhD in the Department of Medical Biophysics at the University of Toronto. He studies how statins can be used to treat cancer. To learn more about Joseph and his research, check out our members page.

References

[1] Formenti & Demaria (2009). Systemic effects of local radiotherapy. Lancet Oncol 10:718-726.

[2] Sharma & Allison (2015). Immune checkpoint targeting in cancer therapy: Toward combination strategies with curative potential. Cell 161:205-214.

[3] Kang et al. (2016). Current clinical trials testing the combination of immunotherapy with radiotherapy. J Immunother Cancer doi: 10.1186/s40425-016-0156-7.

[4] Postow et al. (2012). Immunologic correlates of the abscopal effect in a patient with melanoma. N Engl J Med 366:925-931.

[5] Dewan et al. (2009). Fractionated but not single-dose radiotherapy induces an immune-mediated abscopal effect when combined with anti-CTLA-4 antibody. Clin Cancer Res 15:5379-5388.

[6] Vanpouille-Box et al. (2017). DNA exonuclease Trex1 regulates radiotherapy-induced tumour immunogenicity. Nat Commun doi: 10.1038/ncomms15618.

Wielding a Double-Edged Sword: Oncolytic Viruses in Cancer Therapy

By: Martin Smith, PhD

Oncolytic therapy blog pictureYou know the feeling…  It could start with a nagging headache.  Or, it could be the flush feeling of an oncoming fever.  Whatever it may be, many of us can relate to the symptoms of an impending viral infection. But, what if those same symptoms became signals of life saving treatments?  For some patients in trials of a new cancer therapy, headaches and fevers represent markers of hope. Researchers have now engineered viruses to selectively recognize, infect and kill cancer cells in our body.  These viruses, known as oncolytic viruses, are one of the next-generation cancer immunotherapies being studied to treat cancer.

Viruses can be deadly, and some have devastated the human race.  However, others are being used for oncolytic virus therapy can actually be quite useful.  When virions encounter a living organism something amazing happens. The virus particle will recognize and bind to signals on the surface of the host cell.  Once bound, the virus enters the cell where it hijacks the internal cellular machinery to replicate – making more copies of itself.  Unchecked, replication of the virus can cause the cell to explode . This releases the cell contents, including many new virus particles, which go on to repeat the infection cycle.  This self-perpetuating behavior is common in the virus life cycle and is exactly what cancer researchers want to take advantage of when programming oncolytic viruses to preferentially target cancer cells.

Cancer cells function differently than healthy cells. Scientists have selected viruses that find cancer cells because of their altered function (1).  Or, they have engineered special systems into the virus to recognize specific cancer markers.  Oncolytic viruses happily bind and enter the host and replicate to produce numerous copies of themselves inside the cell.  Gravid with new virus particles, the host cancer cell explodes, spewing out large numbers of cancer killing viral particles to continue the fight.  The cancer cells release their insides during the explosion, activating the immune system to recognize and attack other cancer cells (2).  This activation of the immune system is what leads to common symptoms of viral infection (an infographic illustrating oncolytic viruses can be found here).

It sounds perfect, right? Researchers across the world are definitely excited about oncolytic viruses.  Early stage clinical trials are critical to determine the safety and efficacy (3).  With safety being of utmost importance here, it is important to remember that viruses can be hard to control.  Doctors will consider short-term side effects tolerable as long as they remain manageable.  The long-term behaviour of viral therapies will also be important to understand.  For example, some viral infections can actually lead to cancer.  The human papilloma virus (HPV) has been shown to cause cervical cancer as well as head and neck cancer years after infection.  There is no doubt that determining the effects of oncolytic viruses will be very important as the scientific community approaches drug development.

A cautious approach will be very important in using oncolytic viruses.  The pros and cons associated with the use of these viruses forge a veritable double-edged sword.  Perhaps it is time we pulled that sword from stone and used it in the fight against cancer.

This article was written by Dr. Martin Smith. Dr. Smith completed his PhD at the University of Waterloo studying how proteins can cause cancer. He currently works for the Ontario Brain Institute where he studies brain disease. To learn more about Dr. Smith and his research check out our members page.

References:

(1) Ilkow et al., From Scourge to Cure: Tumour-Selective Viral Pathogenesis as a New Strategy against Cancer, PLOS Pathogens, 2014; 10(1); 1-8.

(2) Chiocca and Rabkin, Oncolytic Viruses and Their Application to Cancer Immunotherapy, Cancer Immunol. Res., 2014; 2(4); 295-300.

(3) Aghi and Martuza, Oncolytic viral therapies – the clinical experience, Oncogene, 2005; 24, 7802-7816.

Teaching Cancer Research to the Next Generation: A Recap of Let’s Talk Cancer 2017

OLYMPUS DIGITAL CAMERAHello everyone! There has been a lot of activity over here at RIOT recently. We thought we would share with you some updates on an incredible event that we just held this past April!

An important aspect of what we do at RIOT is to increase awareness on the progress in cancer research, and that includes reaching out to the younger generation! So, over the past two years, we have been travelling around the GTA, teaching high school classes on cancer biology and what cancer research is like as a potential career option. It’s been an awesome journey for us to meet such bright and motivated students as well as the outstanding teachers that show such an amazing level of commitment and dedication to their students.

These rewarding experiences led us to create a one-day symposium in collaboration with Let’s Talk Science for high school students known as Let’s Talk Cancer. With the support of community donors like SimpliHome, we have been successful in hosting Let’s Talk Cancer events for other RIOT teams across Ontario for the past two years now. Together, we wanted to create a positive and greater learning experience for the exceptionally curious students.

Our event was held in the iconic “Great Hall” at The University of Toronto campus. The space really captured the essence of a historic academic institution with a whimsical nod at Hogwarts! We started the day with an awe-inspiring speech by a young cancer survivor, who shared her personal experiences battling breast cancer. It was humbling to listen to her words, she brought immense perspective to the students and really highlighted the importance of cancer research to all of us.

The day was then filled with lectures from scientific leaders and experts in the various fields of cancer research. We invited scientists to speak on their own research that ranged from ‘Clonality’ and ‘Tumor Microenvironment’ to ‘Personal Oncogenomics’ and ‘Drug Development’. Each lecture was followed by a lively Q&A and then a hands-on activity to engage the students to apply what they learned. A winning team of students, from one of our activities, even had the unique opportunity to tour a stem cell lab! We ended the day with an energetic talk given by a cancer community advocate, who empowered the students with tools to get active and involved in their own community.

Today, cancer touches the lives of people of all ages directly or indirectly. This includes our younger generation – and they want to do something about it, whether it be in advocacy or pursue a career in research and/or medicine. Researchers are still learning more about the complexity of cancer day by day and it is going to take our next generation to make new and lasting discoveries. We hope events like Let’s Talk Cancer inspires the next generation of scientific leaders in our community.

Check out more pictures from the event below!

Can a Genetic Test Help Personalize Prostate Cancer Treatment for Men?

By: Joseph Longo

PCa BRCA2 Blog Image.jpg

Prostate cancer is the most commonly diagnosed cancer among Canadian men, with 1 in 8 men expected to develop the disease in their lifetime. Thanks to advances in early detection and screening, prostate cancer treatments have significantly improved over the years and, if caught early, the 5-year survival rate is nearly 100%. Despite these advancements, over 4000 men still die of prostate cancer each year, making it the third-leading cause of cancer-related death in men.

Treatment for prostate cancer can vary depending on the stage of the disease at diagnosis and how likely the disease is to grow and spread to other parts of the body. Men diagnosed with low-risk prostate cancer tend to go on ‘active surveillance’, where regular check-ups and testing are recommended to closely monitor disease progression. This avoids the need for invasive and aggressive therapies with unwanted side effects in patients with small, slow-growing and asymptomatic disease. Men at higher risk of disease progression are treated with a combination of surgery, radiation therapy and/or hormone therapy. While these lines of therapy are initially effective, approximately one-third of patients will have their cancer return in a more aggressive and lethal form. We currently do not understand why some patients respond to these forms of therapy, while others do not. If we can predict treatment failure, then we can spare patients from unnecessary and ineffective treatments, and potentially offer more personalized and effective treatment options at diagnosis.

A recent study led by a team of researchers from Toronto and Melbourne found that prostate cancer patients with an inherited mutation in the BRCA2 gene tend to have more aggressive and advanced forms of the disease. Mutations in the BRCA2 gene, and its relative BRCA1, are typically associated with an increased risk of breast and ovarian cancers. You may remember the news headlines from 2013 when actress Angelina Jolie underwent a preventative double mastectomy after testing positive for a BRCA1 mutation. What people are less aware of, however, is that inherited mutations in the BRCA2 gene also increase the risk of developing prostate cancer. BRCA1 and BRCA2 are important players in the cell’s ability to repair damage to its DNA. When mutations in these genes prevent them from working properly, it increases the chances of developing cancer.

Prostate tumours in men with an inherited mutation in BRCA2 tend to be more aggressive and have a higher chance of spreading to other parts of the body. These patients are also more likely not to respond to first-line prostate cancer treatments, including surgery and radiation therapy. While the chances of having an inherited BRCA2 mutation are low (less than 1% of the population), testing for this mutation at diagnosis could spare men who are mutant BRCA2-positive from going through therapies that are likely to fail. Instead, these patients may benefit from more aggressive treatment upfront, including chemo- and targeted drug therapies.

This article was written by Joseph Longo. Joseph is currently pursuing a PhD in the Department of Medical Biophysics at the University of Toronto. He studies how statins can be used to treat cancer. To learn more about Joseph and his research, check out our members page.

References

  1. Canadian Cancer Society’s Advisory Committee on Cancer Statistics. Canadian Cancer Statistics 2016. Toronto, ON: Canadian Cancer Society; 2016.
  2. Taylor et al., 2017. Germline BRCA2 mutations drive prostate cancers with distinct evolutionary trajectories. Nature Communications. doi: 10.1038/ncomms13671.

Drug Repurposing for Colorectal Cancer: Redesigning a House Into a Bookstore

By: Douglas Chung

repurposing-drugs-bookstore-dc

What if there was a quicker and cheaper way to bring forth more treatment options for people with cancer? Researchers are trying to do just that by repurposing drugs used for other diseases to treat cancer.

The process of drug development is a costly and lengthy process. Candidate drugs must undergo multiple stages of research and evaluation before they meet the safety and therapeutic requirements to be routinely used in the clinic.

Similar to building a new house, the drug development process requires a novel structural design, construction, and passing of safety regulations. However, once the house is built, it can often be repurposed for different uses including a bookstore, restaurant or dance studio.

Similarly, some approved drugs could be repurposed to treat other diseases than what they were originally intended for. Drug repurposing has gained a lot of interest within the cancer field. The advantage of this approach is that the initial research on how the drug works in the body and its potential side effects have already been done. Drug repurposing dramatically reduces the cost and time it takes to introduce new therapies for cancer patients.

Cimetidine: A treatment for heartburn repurposed for cancer

Cimetidine is an anti-histamine drug used to treat heartburn and peptic ulcers. In 1988, researchers reported that patients with stomach cancer, who happened to be treated with cimetidine for heartburn, demonstrated tumour shrinkage and increased survival [1]. In the past decade, an abundance of animal and clinical trials have provided evidence suggesting that this drug may be a good potential therapy for cancer. But how does a heartburn medication work against cancer?

Cimetidine promotes immune cells to attack tumour

One of the ways cimetidine promotes tumour regression is by promoting immune cells to attack cancer cells. The cells of the immune system are the defenders of our body from not only foreign substances like bacteria and viruses, but also from our own cells that have gone awry. They are capable of recognizing cancerous cells, and subsequently coordinating an organized attack against the tumour.

The best way to describe the epic battle between the immune system and cancer, is to compare it to famous scene in Star Wars when the Death Star (tumour) was attacked by the Rebel Alliance’s X-wing Starfighters (immune cells). Tumours have defensive mechanisms (the Empire’s TIE fighters, or in this case myeloid-derived suppressor cells and regulatory T cells) to stop immune cells from attacking it. This allows the tumour to continue to grow without surveillance.

Several studies have shown that cimetidine targets and shuts down the suppressor cells (Empire TIE fighters) [2,3]. By shutting down suppressor cells, the immune cells are free to attack the tumour with the ultimate goal of destroying that Death Star.

Cimetidine in colorectal cancer

A number of clinical trials have shown promising results using cimetidine to treat colorectal cancer. In a 2002 trial, 64 colorectal cancer patients underwent surgery and were given 5-fluorouracil, a common chemotherapy given after surgery. [4]. Of these 64 patients, 34 patients also received daily doses of cimetidine for a year starting 2 weeks after surgery. Patients were followed for 10 years and those given cimetidine had a higher survival rate.

A recent review which analyzed results from 5 clinical trials, with a total of 421 patients with colorectal cancer (CRC), further confirmed the positive survival benefits of receiving this drug post-surgery [5].

Cimetidine has also shown promise in melanoma, gastric cancer, and renal cell carcinoma [6]. More clinical trials are ongoing to investigate if cimetidine may also provide benefits in other cancer types and whether this is due to the enhancement of the immune system. Time will tell whether this repurposed drug becomes a standard treatment option for colorectal cancer and other cancer types.

This article was written by Douglas Chung. Douglas is a research assistant working in Dr. Pamela Ohashi’s Lab at the Princess Margaret Cancer Centre where he studies how to use the immune system to fight cancer. To learn more about Douglas and his research check out our members page.

References:

  1. To̸nnesen H, Bulow S, Fischerman K, Hjortrup A, Pedersen V.M, Svendsen L, et al. Effect of cimetidine on survival after gastric cancer. The Lancet. 1988;332(8618):990-992.
  2. Zheng Y, Xu M, Li X, Jia J, Fan K, Lai G. Cimetidine suppresses lung tumor growth in mice through proapoptosis of myeloid-derived suppressor cells. Molecular Immunology. 2013;54(1):74-83.
  3. Zhang Y, Chen Z, Luo X, Wu B, Li B, Wang B. Cimetidine down-regulates stability of Foxp3 protein via Stub1 in Treg cells. Human Vaccines & Immunotherapeutics. 2016;12(10):2512-2518.
  4. Matsumoto S, Imaeda Y, Umemoto S, Kobayashi K, Suzuki H, Okamoto T. Cimetidine increases survival of colorectal cancer patients with high levels of sialyl Lewis-X and sialyl Lewis-A epitope expression on tumour cells. British Journal of Cancer. 2002;86(2):161-167.
  5. Deva S, Jameson M. Histamine type 2 receptor antagonists as adjuvant treatment for resected colorectal cancer. [Internet]. 2012 [cited 8 February 2017]. Available from: http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD007814.pub2/full
  6. Pantziarka P, Bouche G, Meheus L, Sukhatme V, Sukhatme V.P. Repurposing drugs in oncology (ReDO)—Cimetidine as an anti-cancer agent. ecancermedicalscience. 2014;8.

A ‘Big Bang’ Theory of Pancreatic Cancer Development

By: Kinjal Desai, Ph.D.

kinjal-blog-picture

Genetic changes causing pancreatic cancer occur all at once, like a big bang, due to massive genetic instability within the cell.

Relatively rare compared to more common cancers, pancreatic cancer is the fourth leading cause of cancer death in both women and men in Canada. Survival beyond 5 years is below 10%. What makes pancreatic cancer so deadly? In part, this is due to the appearance of disease symptoms when the cancer is already at a very advanced stage, despite many efforts toward an early detection. New research out of Toronto now explains why pancreatic cancer is so hard to detect early by providing insight into how it actually develops.

This recent study demonstrates that pancreatic cancer appears to develop spontaneously and rapidly following an event that causes the genome to become highly unstable, leading to thousands of genetic changes happening all at once. This is in stark contrast to the previous views on how cancer forms.

The previous theory is that cancer follows the principles of evolution much like what was identified by the great naturalist Charles Darwin. He proposed a theory of natural selection, that can be described in the following example: a bird has randomly acquired a DNA mutation that causes it to have a very long beak compared to other birds in its flock. Supposing there is a drought in the region and the only seeds available were buried deep in the ground, the once abnormal long-beaked bird now has the most advantage and survives, whereas the shorter-beaked birds in its flock are more vulnerable to starvation. When the long-beaked bird reproduces, it passes on its mutation and the long beak becomes more common or “selected” in the population. However, once the drought passes and long beaks are no longer beneficial to birds for survival, the mutation, offering no particular advantage, may start to once again become a minority in the population.

Darwin’s evolutionary model is frequently seen in cancers too. Cancer cells, which arise from normal cells, randomly acquire mutations in key genes that offer them a growth advantage. Every time a cell acquires a “cancerous” mutation, it gains greater power to grow faster and survive. These mutations, occurring randomly and in a stepwise fashion, eventually create a full-blown cancer.

But this new study from Toronto makes us rethink this theory when it comes to pancreatic cancer. It had previously been observed that pancreatic cancer becomes aggressive almost as soon as it begins forming. This new research suggests that the reason for this is that the disease-causing mutations may be occurring simultaneously with a “big bang” event, rather than in a gradual and stepwise fashion. The authors, led by a team based at the Ontario Institute of Cancer Research (OICR), used a computational method to track the genetic changes in over 100 pancreatic tumour samples to reach their conclusion.

They proposed that pancreatic cancer follows a model of evolution known as “punctuated equilibrium.” The theory was first proposed by Stephen Jay Gould and a colleague, Niles Eldredge, to refer to significant evolutionary changes that occur rapidly in spurts, and which are preceded and followed by long periods of slow and gradual changes described by Darwin’s natural selection. A similar process was also reported in colon cancer, and was referred to as a “big bang” model of cancer growth. This striking analogy is a powerful description of the rapidly changing state from normal to cancerous in certain cases.

This study offers an important new perspective to understanding cancer evolution. By more carefully identifying the different ways in which cancer can evolve in our bodies, researchers and clinicians can better design specific therapies to target them.

This article was written by Dr. Kinjal Desai. She is a postdoctoral research fellow at the Hospital for Sick Children in Toronto, where she works on medulloblastoma, the most commonly occurring malignant brain tumour in children. To learn more about Kinjal and her research check out our members page.

References:

Notta F., Chan-Seng-Yue M., Lemire M., Li Y., Wilson G.W., Connor A.A., Denroche R.E., Liang S-B., Brown A.M.K., Kim J.C., et al. A renewed model of pancreatic cancer evolution based on genomic rearrangement patterns. Nature 538, 378–382 (20 October 2016) | doi:10.1038/nature19823

Sottoriva A., Kang H., Ma Z., Graham T.A., Salomon M.P., Zhao J., Marjoram P., Siegmund K., Press M.F., Shibata D. & Curtis C. A Big Bang model of human colorectal tumor growth. Nature Genetics 47, 209–216 (2015) | doi:10.1038/ng.3214

Darwin, C. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Nature (1859). London: John Murray, 5 (121): 502.

Eldredge, N., Gould, S.J. Punctuated equilibria: an alternative to phyletic gradualism. Models in Paleobiology (1972) pp 82-115.