in the United States, right behind skin cancer.

While it largely affects women, it can also occur in men.

Fortunately, thanks to awareness, early detection, and research,

survival rates have increased

but there's still a lot we're learning.

So how far have we come

in understanding this disease?

Breast cancer affects the cells in the tissue of the breast.

It starts when these cells develop abnormally and begin to divide and accumulate rapidly

eventually forming a lump or mass.

- What happens then is that as the cells in

that tumor to continue to divide

they make additional mistakes in their DNA repair mechanisms

and DNA replication mechanisms

leading to the generation of more mutations.

More mutations generally means more variant cancer.

Hello, my name is Donald McDonnell,

I'm a professor of pharmacology and cancer biology at Duke

School of Medicine and I'm also the co-director of the women's cancer

program at Duke.

Under the breast cancer umbrella, there are three major types.

They're all different, they progress differently, and the treatments for them vary.

- There are cancers which have a protein inside them called the estrogen

receptor, and they are called estrogen receptor-positive breast cancers.

There's a second type of breast cancer which has a protein that sits on

the surface called HER2. And they're called HER2-positive breast cancers.

And then there's a population of breast cancers that neither have the estrogen

receptor, or HER2, and we call those triple-negative breast cancers.

With estrogen receptor breast cancers, a mutation in cell growth allows

the cells to respond to estrogen. Estrogens stimulate growth in a tumor

and as the tumor grows it acquires more mutations. Some risk factors for this

type involve exposure to high levels of estrogen. Those can be from your

environment, having a child later in life or even prolonged use of certain forms of birth control.

- HER2-positive breast cancers are characterized by the

fact that cancer cells of this type have a protein that sits right on the surface

and for all intents and purposes this protein then drives

processes in the cancer cell that drives proliferation and progression.

HER2-positive breast cancers are commonly treated with a drug called

Herceptin, which binds to these proteins, effectively stopping the growth and

spread of the disease.

With triple-negative, these cases occur most

frequently in younger women, particularly those of African American descent, but not exclusively.

Triple-negative breast cancers are so defined because they

don't have the proteins expressed that allows them to be defined as estrogen

receptor or HER2-positive.

And like HER2, there are some promising developments

on the horizon for triple negative.

- We are starting to see some successes in

triple-negative breast cancer with immunotherapy, and recent studies showing

that about 20% of women who are tested on immunotherapy for triple-negative breast cancer

have a positive and durable response.

So, knowing the breakdown of the most common types of breast cancer is a start

but there are also factors that can put someone at a greater risk of contracting this disease.

- So one of the common questions that I get is a researcher is what causes

breast cancer? Why do I have breast cancer? Why do none of my

relatives of breast cancer and I have got breast cancer?

And there's no real simple explanation.

Some risk factors include things such as obesity, estrogen

exposure, and genetics.

In fact, one area that has seen substantial progress is

the understanding of something called familial breast cancer

that is, breast cancer passed down from generation to generation.

In the mid-1990s, two genes

were discovered that, if mutated, actually increase your risk of breast

cancer and these are the notorious Braca 1 and Braca 2 genes.

What is interesting now is that we know quite a lot about how these Braca 1 and Braca 2 genes

influence the pathobiology of breast cancer.

We can actually take a DNA sample

and we can actually test a woman who does not have breast cancer

and ask, is she at risk for familial breast cancer?

While genetic testing is an exciting new development in the field of breast cancer diagnosis,

it's also important to stress that regular screening and early detection are big

factors in breast cancer survival rates as well.

- With the widespread use of mammography

we're now detecting all breast cancer subtypes much much earlier

than we used to.

When breast cancer is usually diagnosed

it's usually limited to one breast in one specific area in the breast,

and for the most part excision will treat this tumor followed by then what's called

adjuvant care, that is, treatments to prevent that cancer coming back again.

But if caught too late breast cancer cells can spread to other

areas of the body, including the bone, liver, and in later stages, the brain.

- From my perspective, the issues that are most important right now

are how do we block metastasis from a primary tumor?

We know that the primary tumor, in and of itself,

is not that harmful within the body

but it seeds cells that go all over the body.

One of the leading theories is that cancers can

develop what Dr. McDonnell describes as a cloak that covers the tumor allowing it

to remain undetected by the body's immune system.

- What we're focused on now is

developing drugs that can peel away this cloak and expose this tumor to the

immune system.

But then there are cases where patients suddenly go into

remission, despite the odds.

This is what Dr. McDonnell and his colleagues

are trying to make sense of

and it could all tie back to the body's immune system.

- Cancers just don't suddenly go away. Something happened within the body to

make that cancer go away. And I think most of us would agree that in large

part these spontaneous remissions are due to responses of the immune system to

that cancer.

Understanding the three main types of breast cancer, their risk

factors, and current treatment options is a first step. But fortunately daily

discoveries and innovations are helping to write a new chapter for this disease.

- Right now, I think we effectively manage and we effectively treat the disease, and

people are living longer with this disease with a very good quality of life.

I think if we are successful in harnessing the immune system and

understanding why breast tumors evade humoral immunity, that we will start

hearing the word "cure" more frequently.