CANCER ASSOCIATED THROMBOSIS CLINIC INFORMATION LEAFLET
If you are reading this, it is most likely that you or a loved one has been given
an appointment to attend the cancer associated thrombosis clinic. This is a
specialist clinic that manages people with cancer who have been diagnosed
with a blood clot or thrombosis.
The clinic is held once a week on a Monday morning in main outpatients at
Velindre Cancer Centre. You will receive an appointment shortly but if you
have any questions please contact the clinic secretary Jo Sulman on 02920
615888.
This leaflet has been written to explain a little about cancer associated
thrombosis and answer any questions you may have prior to your clinic
appointment.
What is cancer-associated thrombosis (CAT)?
Cancer Associated Thrombosis or CAT for short is the term used to describe a
clot or venous thromboembolism (VTE) that occurs in someone with cancer.
In what ways does it differ to someone who has VTE but does not have
cancer?
Several things differ about CAT compared to VTE in non-cancer patients. These
include the cause of the clot, the diagnosis and even the treatment. These shall
be explained in more detail later.
How common is CAT?
CAT is very common; up to 15% of cancer patients may get CAT at some point
during their cancer journey. Someone with cancer is seven times more likely to
get a CAT than a similar patient without cancer.
Why do people get CAT?
The reasons that any person gets a VTE are divided into
 Stasis (sluggish blood flow)
 Endothelial damage (damage to the lining of the body’s blood vessels)
 Hypercoagulability (sticky blood)
There are several factors specific to cancer that makes a cancer patient more
likely to develop a blood clot.
The most significant of these are to do with hypercoagulability (sticky blood).
Studies have shown that the cancer itself releases molecules into the blood,
which make the bloods coagulation (clotting) system more active.
Some cancers are more prone to clots than others. For example patients with
cancer of the pancreas, lung and ovary are best known to cause clots whilst
breast and prostate cancer less so.
Also, it appears that cancers that have spread to other parts of the body
(metastatic cancer) are at greater risk of CAT than similar cancers, which have
not spread.
Half of all cases of CAT are in patients with metastatic cancer.
Can anything else increase the risk of CAT?
Yes. There is evidence to show that treatments such as chemotherapy, cancer
surgery, radiotherapy and hormone treatments can increase the risk of blood
clots.
When does CAT most commonly occur?
Over 50% of CATs occur in the first three months of being diagnosis.
This is most likely because this will coincide with the time patients receive their
cancer treatments such as surgery and chemotherapy.
How is CAT treated?
The way we treat CAT differs to the treatment of VTE in non-cancer patients.
Normally VTE is treated with three to six months of an anticoagulant (blood
thinner) called warfarin, which is taken as a tablet each day.
Research has shown that when warfarin is used to treat CAT, there is a higher
rate of bleeding compared to non-cancer patients on warfarin. Also CAT is
associated with a higher than normal rate of clot recurrence.
Therefore we treat CAT with an anticoagulant called low molecular weight
heparin (LMWH). There are several different brands of LMWH used by doctors,
which include
 Dalteparin (Fragmin)
 Enoxaparin (Clexane)
 Tinzaparin (Innohep)
This medicine is given as a daily injection under the skin, similar to someone
with diabetes using insulin. Whilst people would usually prefer a tablet to an
injection, LMWH is used because it reduces the recurrence of VTE by 50%
(half).
To put this in perspective:
 If 100 patients with CAT are given warfarin, then 17 patients will get a
recurrence over six months.
 If 100 patients with CAT are given LMWH, then 9 patients will get a
recurrence over six months.
In simple terms LMWH reduces recurrent blood clots by half compared
to warfarin.
What about these new tablet anticoagulants? Why aren’t they used in CAT?
There are three new tablet anticoagulants known as NOACS, which stands for
Novel Oral Anticoagulants. These are
 Dabigatran
 Rivaroxaban
 Apixaban
All three NOACS have been studied in clinical trials and compared with
warfarin.
All studies have shown them to be as good as warfarin and are recommended
in the treatment of deep vein thrombosis (DVT) and pulmonary embolus (PE).
The studies included a small number of cancer patients.
This makes them appealing in the cancer setting since they would not require
an injection. However these studies have only demonstrated these tablets to
be as good as warfarin (which we know is not as good as LMWH).
No studies have been done comparing a NOAC with LMWH and therefore
there isn’t enough information to conclude that NOACS are currently as good
as LMWH in the treatment of CAT.
How long should CAT be treated for?
Most patients will need to be treated with LMWH for six months.
However, there is a body of opinion that patients with ongoing cancer may still
be at risk of CAT and should remain on treatment.
Therefore the doctor may sometimes treat the patient beyond six months.