Fighting a contagious cancer Elizabeth Murchison

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 water 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 and marsupial is a

mammal with a pouch like a kangaroo the

Tasmanian Devil got its name from the

terrifying nocturnal scream that it

makes

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 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 always was

incredibly exciting when we got a chance

to see that has Manian 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 it has minion

devil with a large tumour 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 mouths 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

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 still feeding through little

baby Tasmanian devils in her pouch of

course they died along with her mother

they too young to survive without their

mother in fact in the area where she

comes from more than 90% of the

Tasmanian Devil population has already

died of this disease scientists around

the world were intrigued by this cancer

this infectious cancer that were

spreading through that Hasmonean devil

population and our minds immediately

turns 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 and 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 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 is spreading through our bodies

are eating away at our tissues leads to

the death of the cancer patient and also

to the death of the cancer itself so

cancer can 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

cancers DNA this has worked for many

people but I’m going to explain it

through in a confirmatory experiment

that I did a few years ago 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

Jonases 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’s 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 are as

different from each other as you and the

person sitting next to you what this

told us was that Jonas’s 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 Jonah’s is clearly a

male so how come a tumor that that arose

from the cells of another individual are

growing on Jonas’s 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 are broken free of

that first devils 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 remembered 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 that actually physically implants

living cancer cells into the next devil

so the jima continues to grow 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

Kimber’s penis the vet diagnosed this as

transmissible venereal tumor a sexually

transmitted cancer that affects dogs and

just as that has Manian devil cancerous

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 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 than the and at

halls 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 crude cancers be

contagious between people well this is a

question which fascinated Chester

Southern a cancer doctor in the 1950s

and 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. southern

in 1957 injecting cancer into a

volunteer who in this case was an inmate

in Ohio State Penitentiary most of the

people that doctor saw them 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 is eckle issues aside is that

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

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

cancers 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