How to pronounce "chomp"

Everyone's familiar with cancer,

but we don't normally think of cancer

as being a contagious disease.

The Tasmanian devil has shown us

that, not only can cancer be a contagious disease,

but it can also threaten

an entire species with extinction.

So first of all, what is a Tasmanian devil?

Many of you might be familiar with Taz, the cartoon character,

the one that spins around and around and around.

But not many people know

that there actually is a real animal called the Tasmanian devil,

and it's the world's largest carnivorous marsupial.

A marsupial is a mammal with a pouch

like a kangaroo.

The Tasmanian devil got its name

from the terrifying nocturnal scream that it makes.

(Screaming)

(Laughter)

The Tasmanian devil is predominantly a scavenger,

and it uses its powerful jaws

and its sharp teeth

to chomp on the bones of rotting dead animals.

[The] Tasmanian devil is found only on the island of Tasmania,

which is that small island

just to the south of the mainland of Australia.

And despite their ferocious appearance,

Tasmanian devils are actually

quite adorable little animals.

In fact, growing up in Tasmania,

it always was incredibly exciting

when we got a chance to see

a Tasmanian devil in the wild.

But the Tasmanian devil population

has been undergoing a really extremely fast decline.

And in fact, there's concern

that the species could go extinct in the wild

within 20 to 30 years.

And the reason for that

is the emergence of a new disease,

a contagious cancer.

The story begins in 1996

when a wildlife photographer took this photograph here

of a Tasmanian devil

with a large tumor on its face.

At the time, this was thought to be a one-off.

Animals, just like humans,

sometimes get strange tumors.

However, we now believe

that this is the first sighting of a new disease,

which is now an epidemic spreading through Tasmania.

The disease was first sighted

in the northeast of Tasmania in 1996

and has spread across Tasmania like a huge wave.

Now there's only a small part of the population,

which remains unaffected.

This disease appears first as tumors,

usually on the face or inside the mouth

of affected Tasmanian devils.

These tumors inevitably grow into larger tumors,

such as these ones here.

And the next image I'm going to show

is quite gruesome.

But inevitably, these tumors progress

towards being enormous, ulcerating tumors like this one here.

This one in particular sticks in my mind,

because this is the first case of this disease

that I saw myself.

And I remember the horror of seeing this little female devil

with this huge ulcerating, foul-smelling tumor

inside her mouth

that had actually cracked off her entire lower jaw.

She hadn't eaten for days.

Her guts were swimming with parasitic worms.

Her body was riddled with secondary tumors.

And yet, she was feeding three little baby Tasmanian devils

in her pouch.

Of course, they died along with the mother.

They were too young to survive without their mother.

In fact, in the area where she comes from,

more than 90 percent of the Tasmanian devil population

has already died of this disease.

Scientists around the world

were intrigued by this cancer,

this infectious cancer,

that was spreading through the Tasmanian devil population.

And our minds immediately turned to cervical cancer in women,

which is spread by a virus,

and to the AIDS epidemic,

which is associated with a number of different types of cancer.

All the evidence suggested that this devil cancer

was spread by a virus.

However, we now know -- and I'll tell you right now --

that we know that this cancer is not spread by a virus.

In fact, the infectious agent of disease in this cancer

is something altogether more sinister,

and something that we hadn't really thought of before.

But in order for me to explain what that is,

I need to spend just a couple of minutes

talking more about cancer itself.

Cancer is a disease

that affects millions of people around the world every year.

One in three people in this room

will develop cancer at some stage in their lives.

I myself had a tumor removed from my large intestine

when I was only 14.

Cancer occurs

when a single cell in your body

acquires a set of random mutations in important genes

that cause that cell to start to produce

more and more and more copies of itself.

Paradoxically, once established,

natural selection actually favors

the continued growth of cancer.

Natural selection is survival of the fittest.

And when you have a population of fast-dividing cancer cells,

if one of them acquires new mutations,

which allow them to grow more quickly,

acquire nutrients more successfully,

invade the body,

they'll be selected for by evolution.

That's why cancer is such a difficult disease to treat.

It evolves.

Throw a drug at it,

and resistant cells will grow back.

An amazing fact is that,

given the right environment and the right nutrients,

a cancer cell has the potential

to go on growing forever.

However cancer is constrained

by living inside our bodies,

and its continued growth,

its spreading through our bodies

and eating away at our tissues,

leads to the death of the cancer patient

and also to the death of the cancer itself.

So cancer could be thought of

as a strange, short-lived, self-destructive life form --

an evolutionary dead end.

But that is where the Tasmanian devil cancer

has acquired an absolutely amazing

evolutionary adaptation.

And the answer came from studying

the Tasmanian devil cancer's DNA.

This was work from many people,

but I'm going to explain it through a confirmatory experiment

that I did a few years ago.

The next slide is going to be gruesome.

This is Jonas.

He's a Tasmanian devil that we found

with a large tumor on his face.

And being a geneticist,

I'm always interested to look at DNA and mutations.

So I took this opportunity

to collect some samples from Jonas' tumor

and also some samples from other parts of his body.

I took these back to the lab.

I extracted DNA from them.

And when I looked at the sequence of the DNA,

and compared the sequence of Jonas' tumor

to that of the rest of his body,

I discovered that they had a completely different genetic profile.

In fact, Jonas and his tumor

were as different from each other

as you and the person sitting next to you.

What this told us was that Jonas' tumor

did not arise from cells of his own body.

In fact, more genetic profiling

told us that this tumor in Jonas

actually probably first arose

from the cells of a female Tasmanian devil --

and Jonas was clearly a male.

So how come

a tumor that arose from the cells of another individual

is growing on Jonas' face?

Well the next breakthrough

came from studying hundreds of Tasmanian devil cancers

from all around Tasmania.

We found that all of these cancers

shared the same DNA.

Think about that for a minute.

That means that all of these cancers

actually are the same cancer

that arose once from one individual devil,

that have broken free of that first devil's body

and spread through the entire Tasmanian devil population.

But how can a cancer spread in a population?

Well the final piece of the puzzle came

when we remember how devils behave when they meet each other in the wild.

They tend to bite each other,

often quite ferociously and usually on the face.

We think that cancer cells

actually come off the tumor, get into the saliva.

When the devil bites another devil,

it actually physically implants living cancer cells into the next devil,

so the tumor continues to grow.

So this Tasmanian devil cancer

is perhaps the ultimate cancer.

It's not constrained by living within the body that gave rise to it.

It spreads through the population,

has mutations that allow it to evade the immune system,

and it's the only cancer that we know of

that's threatening an entire species with extinction.

But if this can happen in Tasmanian devils,

why hasn't it happened in other animals

or even humans?

Well the answer is, it has.

This is Kimbo.

He's a dog that belongs to a family in Mombasa in Kenya.

Last year, his owner noticed some blood

trickling from his genital region.

She took him to the vet

and the vet discovered something quite disgusting.

And if you're squeamish, please look away now.

He discovered this,

a huge bleeding tumor

at the base of Kimbo's penis.

The vet diagnosed this as transmissible venereal tumor,

a sexually transmitted cancer

that affects dogs.

And just as the Tasmanian devil cancer is contagious

through the spread of living cancer cells,

so is this dog cancer.

But this dog cancer is quite remarkable,

because it spread all around the world.

And in fact, these same cells

that are affecting Kimbo here

are also found affecting dogs

in New York City,

in mountain villages in the Himalayas

and in Outback Australia.

We also believe this cancer might be very old.

In fact, genetic profiling tells

that it may be tens of thousands of years old,

which means that this cancer

may have first arisen

from the cells of a wolf

that lived alongside the Neanderthals.

This cancer is remarkable.

It's the oldest mammalian-derived life form that we know of.

It's a living relic

of the distant past.

So we've seen that this can happen in animals.

Could cancers be contagious between people?

Well this is a question

which fascinated Chester Southam,

a cancer doctor in the 1950s.

Ad he decided to put this to the test

by actually deliberately inoculating people

with cancer from somebody else.

And this is a photograph of Dr. Southam in 1957

injecting cancer into a volunteer,

who in this case was an inmate

in Ohio State Penitentiary.

Most of the people that Dr. Southam injected

did not go on to develop cancer

from the injected cells.

But a small number of them did,

and they were mostly people who were otherwise ill --

whose immune systems were probably compromised.

What this tells us,

ethical issues aside,

is that ...

(Laughter)

it's probably extremely rare

for cancers to be transferred between people.

However, under some circumstances,

it can happen.

And I think that this is something

that oncologists and epidemiologists

should be aware of in the future.

So just finally,

cancer is an inevitable outcome

of the ability of our cells

to divide

and to adapt to their environments.

But that does not mean that we should give up hope

in the fight against cancer.

In fact, I believe, given more knowledge

of the complex evolutionary processes that drive cancer's growth,

we can defeat cancer.

My personal aim

is to defeat the Tasmanian devil cancer.

Let's prevent the Tasmanian devil

from being the first animal

to go extinct from cancer.

Thank you.

(Applause)