Tag Archives: breast cancer

Of Mice and Mammaries, Part 4: From animal models to human therapies

In light of Breast Cancer Awareness Month, Justin Varholick traces how mice have helped breast cancer research over the past century. Over the past month, in Parts 1, 2, and 3 of this series, he discussed how scientists began studying mammary tumors in mice and how they have advanced their study to better understand human breast cancer. In the fourth post of this series, he looks at how a hormonal therapy was discovered and how scientists are paving a way for new and effective discoveries in patient derived xenografts.

Breast cancer comes in many forms and can be detected at different stages throughout a women’s life. After a doctor diagnoses the type of breast cancer, they can suggest surgery and/or therapies. Surgery is the common practice to remove breast tumors and is also referred to as lumpectomy (breast-conserving surgery) or mastectomy (whole breast removal); and may also involve removal of lymph nodes. Doctors will then advise their patients to have radiation therapy, chemotherapy, hormonal therapy, or targeted therapy – this is to assure that the breast cancer does not return.

Types of Breast Cancer Surgery Therapies
Invasive Breast Cancer (stages I-IV) Lumpectomy or Mastectomy depending on stage Radiation along with chemo or other drug therapies
Ductal Carcinoma in situ Lumpectomy or Mastectomy depending on degree Hormone therapy for 5 years
Lobular carcinoma in situ No surgery May consider hormone therapy
Inflammatory breast cancer Mastectomy Chemo before and radiation after surgery
Breast cancer during pregnancy Lumpectomy or Mastectomy Any therapy after delivery
Triple-negative breast cancer Mastectomy Chemotherapy may be useful

(Information from American Cancer Society)

Because chemotherapy and radiation therapy are common methods used to treat many different types of cancers post- and pre-surgery, we will focus on the most widely used therapy that specifically targets breast tumors – Tamoxifen.

History of Tamoxifen, a targeted hormonal therapy

The history of Tamoxifen begins around the same time the first mammary tumors in mice were discovered. In 1896, pioneering cancer surgeon Dr. George Beatson discovered that he could extend the lives of breast cancer patients by surgically removing their ovaries. This surgery was then replicated in mice in 1916. The reason the removal of ovaries helped breast cancer patients was because ovaries are major sources for producing the hormone, estrogen. When some forms of breast tumors are exposed to estrogen they can grow larger and spread further than when no or lower levels of estrogen are present. This is because the tumors have estrogen receptors. If estrogen is helping the tumors grow, then removing estrogen would be an ideal solution.

Estrogen can be removed in two different ways; by blocking it from binding to receptors on the tumors, or by reducing its production in the body – which is what happened when surgeons removed the ovaries. Tamoxifen works by blocking estrogen receptors on breast cancer cells.

Image from River Pharmacy

Tamoxifen has a very unusual origin story. Scientists first began developing the drug in the 1960s as a contraceptive to reduce fertility by blocking estrogen. When they tested it in rats, the rats were less fertile. But when tested in mice, the mice were more fertile. This paradoxical effect made scientists uncertain about how it would affect humans. Through clinical trials in the early 1970s, scientists determined that the drug also increased fertility in human women, and was thus marketed to induce ovulation in women and also to treat breast cancer in post-menopausal women because of how it worked to block estrogen receptors.

The reason this anti-estrogen drug can increase fertility rather than be used as a contraceptive is because it blocks estrogen from attaching to estrogen receptors. This means there is more estrogen in the body, thus increasing fertility. This is also why Tamoxifen is more useful in post-menopausal women than pre-menopausal women.

Tamoxifen isn’t the only anti-estrogen drug that is used to treat breast cancer. The American Cancer Society is a great source for more information about other current treatments such as aromatase inhibitors and ovarian suppression.

Patient Derived Xenograft, a future therapy

Now I turn to a future breast cancer therapy – patient derived xenografts. We have previously discussed patient derived xenografts in one of our research roundups. These xenografts work by taking tumor cells from patients and directly implanting them into mice. These patient tumors in the mice can then be studied to learn how they might grow/spread, and which therapies might be most effective.

One reason this tool is so important is because it can provide a more personalized approach towards caring for the patient. It is even more important for breast cancer because breast tumor cells grow and spread differently for each patient – the cancer is very diverse. By growing each patient’s unique cancer, we may be able to tailor treatments to specific patients and learn more about breast cancer in general.

Patient derived xenografts, however, are not a cure-all and there is still much we need to research. As covered in the research roundup, the tumor cells may grow differently in mice than they would in a human. Thus, just because a therapy might work for a mouse it does not necessarily mean it will work for a human. Also, for these xenografts to be effective, we need to reduce the amount of time it takes for scientists to test the tumors in the mice without compromising the translational power of the mice. For example, we could increase how fast the tumors spread in the mice, but that may compromise the tumors to a point where they are no longer similar to the tumors in the patient.

The end of a series…

We hope that you have enjoyed this series, “Of Mice and Mammaries.” Not only should this series educate our readers about breast cancer and animal research, it should also demonstrate the importance of animal research in treating disease.

In the early 1900s the mouse was viewed as an unsuitable model for humans because the virus, MMTV, that spread breast cancer in mice was never identified in humans. But through further research, scientists could generate genetically engineered (GE) mice and through rigorous validation, provided evidence of the suitability of these (GE) mice as models for humans. They then could test drug therapies, such as Tamoxifen, on these animal models and later develop future patient derived xenograft models.

When research is in early stages, it is often difficult to determine when and how it will help humans or other animals. Sometimes, research is based on an idea. But, over time the idea may grow as evidence accumulates with respect to its relevance and efficacy, and, in turn, may continue in a new direction. These new directions often lead to great breakthroughs, and these breakthroughs, in turn, may help humans.  The story of mice and mammaries is a great example of this process.

Justin Varholick


  1. Jordan VC. (2003). Tamoxifen: a most unlikely pioneering medicine. Nature Reviews, Drug Discovery. 2.
  2. Whittle JR, Lewis MT, Lindeman GJ, Visvader JE. (2015). Patient-derived xenograft models of breast cancer and their predictive power. Breast Cancer Research. 17(17).

Of Mice and Mammaries, Part 2: Breast cancer in a dish?

In light of Breast Cancer Awareness Month, Justin Varholick traces how mice have helped breast cancer research over the past century. In the second post of this 4-part series, we look at advances made from 1960 to 1975 when scientists were studying a virus in the milk.

Last week, in Part 1 of this series, we discussed how scientists from the early 1900s studied the growth and spread of mammary tumors in mice. We also walked through an experiment discovering how the breast milk from mother mice carried “something” that was more responsible for breast cancer than the genes the mother had passed down to her pups. This week we learn how scientists determined that this new “something” was a virus, and this virus could only be found in mice – it was never found in humans.

1940 to 1960 — What’s in the milk?

After Dr. John Bittner found out that there was “something” in the milk, many scientists wanted to figure out what it was. A first thought was to filter the milk and see if it still showed the same effects as Dr. Bittner’s experiments. Scientists took very special filters used to filter out bacteria, and ran mouse milk from “high tumor” mothers through these filters. Despite filtering, the results remained the same – filtered milk from “high tumor” mothers still led to tumors in pups fed the milk.

Then in the early 1950s scientists started using electron microscopes to compare “high-tumor” mouse breast milk with normal “low tumor” mouse breast milk. The electron microscopes gave scientists the power to magnify the milk 2,000,000x the normal size – magnification beyond what the bacteria filters could filter out. After comparing the types of milk, Dr. Leon Dmochowski found many small particles in the “high tumor” milk and very few of these particles in the “low tumor” milk. After other scientists repeated these experiments, they concluded that these particles were the “something” in the milk that may be responsible for tumors in the pups. Many scientists looked for these particles in human breast tissue and milk, but could never find it – only mice have this “something” in the milk. It was interesting, however, that the particles were in both “high tumor” mothers and “low tumor” mothers, albeit in different amounts, which indicated that both types of mothers were at risk to have the mammary tumors – “high tumor” mothers just had a higher risk.

While all this science with electron microscopy was going on, scientists studying mammary tumor cells in mice determined that the something in the milk acted very much like a virus and gave it the name mouse mammary tumor virus, or MMTV for short.

Cover of “Immunity against the mouse mammary tumor virus” by Paula Creemers. Electron microscope image of MMTV with a sketch of two mice with mammary tumors.

1960 to 1975 — Can we grow the milk virus in a dish?

Now that scientists had established that a virus in the milk was responsible for mammary tumors in mice, they wanted to see if they could grow the virus in a petri dish. Scientists had already grown viruses in a dish that were responsible for cancer in chickens, and other viruses that were responsible for skin cancer in humans, so they believed they would be able to grow MMTV in the dish. Unfortunately, growing the milk virus dish proved very difficult.

In the 1970s many scientists tried to grow the virus in a dish and were unsuccessful. One group of scientists at the Cancer Research Genetics Laboratory (CRGL) of the University of California, Berkeley showed that the virus could be grown in a dish, but it was too cumbersome for many scientists to use for research. Because MMTV could not be easily grown in a dish, scientists interested in mammary tumors in mice knew they had to find a new method if they wanted to continue using mice to understand more about breast cancer.

To be continued…

Tune in next week, to learn how scientists started using new methods with stem cells to make genetically engineered mice and how they validated that the mouse could be used as a model for humans!

Justin Varholick


  1. Cardiff R, Kenney N. (2011). A compendium of the mouse mammary tumor biologist: From the initial observations in the house mouse to the development of genetically engineered mice. Cold Spring Harb Perspect Biol. 3(6).


Of Mice and Mammaries, Part 1: There’s something in the milk

In light of Breast Cancer Awareness Month, Justin Varholick traces how mice have helped breast cancer research over the past century. In the first post this 4-part series, we look at advances made from 1854 to 1940, including the understanding of the role of breast milk in causing certain types of tumors. 

Image credit: Jackson Labs

Breast cancer is one of the most serious forms of cancer facing women. Each year, over 300,000 women in the U.S. will be diagnosed with breast cancer, and it is estimated that 40,610 women will die from it in 2017 alone. Thankfully, death rates from breast cancer have dropped almost 40% from 1989 to 2015, and there are over 3.1 million breast cancer survivors living in the U.S. today.

Breast cancer grows and spreads through many stages, and can start in different parts of the breast. Some types of breast cancer cause lumps, others form no lumps. Some forms of it spread very quickly throughout the body, while others spread more slowly. Because breast cancer spreads and forms at different rates and in different areas of the breast, treating it is no easy task. It is also unlikely that we will one day have a “cure” for breast cancer — one size cannot fit all.

Despite the complicated nature of breast cancer, scientists feel a responsibility to understand it as much as possible in efforts to find new treatment methods and forms of a cure. Over the years they have made great strides in their research by studying mice. These mice serve as an essential step between early research on mammary cells and clinical trials in humans.

Over the course of this month, I will highlight some of the key findings scientists have discovered about breast cancer through their studies in mice.

1854 to 1903 — The first mouse mammary tumors

The first discovery of a mammary tumor in a mouse was in 1854. In these early days, scientists were able to find tumors spontaneously growing in female mice kept as pets and in the wild. Although they were able to detect and describe these tumors, it was difficult to understand where they came from, and how they grew and possibly spread or metastasized.

Thankfully in 1903, Dr. Carl Jensen developed a line of “high tumor” mice that readily grew mammary tumors, which could be easily transplanted to other mice. By transplanting the tumors in other mice, they could measure how and where the tumors spread, in otherwise healthy mice.

During this time in history, 1.2* women per 1,000 died from breast cancer in the U.S. Today it is around 0.13 women per 1,000. (*at this time we only had reports on the number of white women in the U.S.).

1933 to 1940 — There’s something in the milk

After bringing mice into the laboratory and thoroughly studying their biology, a great discovery was made — there was something in the milk. This discovery was made by Scientists at Jackson Laboratories, in Bar Harbor, Maine. They bred “high tumor” mice with “low tumor”* mice and found that offspring were more likely to get mammary tumors if they had a “high tumor” mother. Although some scientists were able to replicate this finding in other labs, very few were convinced there was something in the milk — they believed it was passed down through the genes. (* an extremely low number of “low tumor” mice were found with mammary tumors; because of this scientists could not call them “no tumor” mice.)

To answer whether there was either something in the genes or the milk, Dr. John J. Bittner did a more complex study 3 years later. In this key study, Bittner cross-fostered mouse pups from “high tumor” and “low tumor” mice to opposite mothers (see diagram). This method allowed him to determine whether the parent’s genes or the foster mother’s milk lead to mammary tumors. If it was the genes then “high tumor” offspring would have tumors whether they had “high tumor” or “low tumor” foster parents. If it was the milk then any offspring nursed by “high tumor” mothers would get tumors.

Through this experiment, Bittner found out that milk was a key factor. “Low tumor” pups cross-fostered to “high tumor” mothers had many mammary tumors, while “high tumor” pups cross-fostered to “low tumor” mothers had very few tumors. “High tumor” pups nursed by their own mothers, however, had the highest rates of tumor growth. It didn’t always matter who the parents were, it also mattered who nursed the pups. This verified that indeed there was something in the milk. This something was labeled as the Mouse Mammary Tumor Virus (MMTV).

Dr. Bittner was often heard stating that he only studied the milk because nobody else wanted it — they all wanted to study the genes.

To be continued…

Tune in next week to read what we learned about the milk virus, MMTV, and what we did with this new power!

Justin Varholick


  1. Cardiff R, Kenney N. (2011). A compendium of the mouse mammary tumor biologist: From the initial observations in the house mouse to the development of genetically engineered mice. Cold Spring Harb Perspect Biol. 3(6).
  2. Holen I, Speirs V, Morrissey B, Blyth K. (2017). In vivo models in breast cancer research: progress, challenges and future directions. Dis Model Mech. 10(4).
  3. Tarone RE, Chu KC. (1992). Implications of birth cohort patterns in interpreting trends in breast cancer rates. J Natl Cancer Inst. 84(18).

The First Decade of the Human Genome: What’s on the Horizon?

To mark the 10th anniversary of the sequencing of the human genome the BBC aired a documentary yesterday evening entitled “Miracle cure: a decade of the human genome” that can be viewed on the BBC iPlayer.  It was an enjoyable look at what has been accomplished since the famous announcement at the White House in June 2000, and while I think the program could have done with exploring some of the science in more depth, it gave a good overview and didn’t shrink from the sheer complexity of many of the questions that face scientists who are now attempting to understand the genome.

Sophie Longton holds a vial containing a gene therapy treatment that may one day cure her of cystic fibrosis. Image Courtesy of the BBC.

The program followed three individuals as they sought to understand what impact the knowledge gained from studying the genome could have on illnesses that have affected them, breast cancer, cystic fibrosis, and alcoholism, and what basic, applied, and clinical research is currently underway. The case of a woman whose breast cancer is linked to a defective BRCA1 gene turned to discussion of the potential for the development of personalized medicine – treatments that are tailored to the genetic makeup of an individual patient’s cancer cells. Animal research plays a very important role in the development of targeted therapies that can be used in personalized medicine, and an early example of this is the drug Herceptin, which is used to treat cancers that express the HER2 gene.

The cystic fibrosis thread focussed on the development of gene therapy and clinical trials now underway under the direction of Professor Eric Alton of the UK Cystic Fibrosis Gene Therapy Consortium. These gene therapy trials use lipid spheres to transport working copies of the CFTR gene – defective in cystic fibrosis – to the lungs of patients, and the particular lipid formulation used in these trials, known as  GL67A was selected after careful evaluation against other candidates, first in CF mice and then in sheep (1).  Mice models of cystic fibrosis have helped researchers to understand more about the disease and to assess therapies, but until very recently research has been hampered by the lack of a large animal model of cystic fibrosis that models the lung pathology of cystic fibrosis.  This situation finally changed in 2008 when scientists at the Universities of Iowa and Missouri produced genetically modified pigs that lack the CFTR gene and develop all the pathologies that are characteristic of cystic fibrosis in humans. This new animal model for cystic fibrosis will be very useful for evaluating the safety and efficiency of new gene therapy techniques as the science advances.

Finally the thread on the influence on genetics on alcoholism was a reminder of just how complex the interaction between an array of genetic variations and the environment can be, and that while it may be possible to identify factors that predispose an individual towards a particular condition it is often difficult, if not impossible, to identify a single cause that tips the balance. Considering the enormous damage caused to society by addiction, and the high failure rate of addiction treatment programs, there is no doubt that addiction research is a neglected area within biomedical science.  This is sad because research into the physiological underpinnings of addiction can aid the development of more effective treatment programs. Hopefully the identification of genes that predispose certain individuals to addiction will help society to realise that science can make an important contribution to solving this medical and social problem.

Paul Browne

1)       Griesenbach U, Alton EW; UK Cystic Fibrosis Gene Therapy Consortium. “Gene transfer to the lung: lessons learned from more than 2 decades of CF gene therapy.” Adv Drug Deliv. Rev. Volume 61(2), Pages 128-39 (2009) DOI: 10.1016/j.addr.2008.09.010.

Herceptin: When personalized medicine and animal research meet.

Personalized medicine is very popular among medical researchers these days, and it’s not hard to see why. By tailoring treatment to fit an individual patient, for example by using information about their genetic makeup, scientists hope to make treatments more effective while at the same time avoiding or minimizing adverse effects.

Anti-vivisectionist Dr. Greek writes about personalized medicine as if one could do this work without relying on animal research at all.

For example, he writes:

When will personalized medicine become a reality?

We are already seeing it, with breast cancer being a prime example. Breast cancer treatment is now determined in part based on a patient’s genetic makeup. About 25-30 percent of breast cancer patients overexpress the HER2 oncogene, which is a gene involved in the development of cancer. The overexpression results in an increase in the replication of the cancer cells. Physicians are now able to identify which breast cancer patients overexpress HER2 and give them Herceptin, a monoclonal antibody that inhibits HER2

This is true…  but where did Herceptin come from?   Does he know?

Herceptin, a humanized mouse monoclonal antibody. Image courtesy of Andrey Ryzhkov.

The basic research that led to the development of Herceptin (Trastuzumab) goes back to work by Milstein and Kohler who discovered the potential for using antibodies to fight disease.    They developed the first methods to produce monoclonal antibodies using mice.   Both Milstein and Kohler went on to win the Nobel Prize partly for this work.

Harold Varmus (now back as Director of the National Cancer Institute) showed that disturbances in some gene families could turn the cells cancerous.  He also went on to win the Nobel Prize for this work.  Robert Weinberg subsequently discovered in rats that a mutant gene (named “neu”) encoding a tyrosine kinase promoted cancer features in cells, contributing to the development of neuroglioblastoma tumors.

Later, Axel Ullrich and collaborators at Genentech cloned the human HER2/neu gene.  Work at UCLA Dennis Slamon and colleagues showed HER2 over-expression in 25% of patients with aggressive breast cancer.

Through screening studies on monoclonal antibody candidates in vivo in mice implanted with HER-2 positive human tumors the group at Genentech then developed the mouse 4D5 (parent of Herceptin) and showed that 4D5 could suppress the growth of HER2 tumor cells as well as enhance the ability of the host immune system to kill them.   A collaboration between UCLA and Genentech then demonstrated that radio-labeled 4D5 localized to HER2-expressing tumors in both mice and human patients.

With the information obtained from animal experiments, Genentech created Herceptin by humanizing the 4D5 mouse antibody directed at HER2.   The ability of Herceptin to prevent tumor growth was then assessed in mice implanted with HER-2 positive human tumor xenografts, and the concentration of Herceptin required in the blood to achieve anti-tumor activity was determined before starting human clinical trials.

So, you see…  Herceptin was derived from a mouse antibody.

Let me repeat: a mouse antibody!

Clinical trials in humans subsequently showed the effectiveness of Herceptin to treat HER2 positive breast cancer.

Perhaps, Dr. Greek and other animal rights activists should carefully listen to the experts that were actually involved in the process of developing Herceptin (a drug he appears to thinks highly of) which, indeed, benefits so many women battling breast cancer.   A drug derived from mice, and developed in mice.

Here is what Robert Weinberg had to say about Dr. Greek’s views on research:

Dr. Greek says the silliest things, […] implying that people are not studying human tumors, and implying that the kinds of experiments that one can do in mice can be done as well in humans — truly mindless!

I couldn’t have said it better.

Dario Ringach


SSR Heading

On Monday July 20th Tom Holder gave a presentation as part of the President’s Sympozium at the Society for the Study of Reproduction‘s 42nd Annual Meeting. The presentation was attended by around 500 members of the society, ranging from undergraduates up to well established professors. The talk provided suggestions on how to talk about science to those without a science background, as well the importance of speaking out. After the talk a number of members of SSR have been in contact to ask how they can get involved with Speaking of Research’s activities – a positive result all round.


The rest of the conference provided an interesting overview of some of the research going on to tackle illness such as infertility, cancer and endometriosis. Animal models varied from fish and rodents, through to cattle, pigs and primates, with scientists careful to explain why their particular choice of animal was the most suitable for their particular research. GnRH (Gonadotropin-releasing hormone) agonists are a good example of the crucial role that animals have played in fighting disease in reproductive biology. After significant work with monkeys, mice and sheep scientists were able to come up with some of the leading treatments for prostate cancer, breast cancer and endometriosis – such as Leuprolide (Market Name: Viadur/Lupron) and Goserelin

You can read the abstract for Holder’s speech here.