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