Monitoring response to treatment

When you start taking TK inhibitors, you’ll need regular checkups to monitor your response to treatment. At first these may be every week or so but eventually you may only need to go every 2–3 months. You will see your doctor and usually have a blood test and sometimes a bone marrow test.

There are several levels of response to TK inhibitors.

  • A haematological response is when your full blood count , particularly the white blood cell count, goes back to normal and no leukaemia cells can be seen.
  • A cytogenetic response is when the number of Philadelphia chromosomes in the blood and bone marrow goes down.
  • A molecular response measures the level of the BCR-ABL gene in the leukemia cells. A molecular response is when there are only tiny amounts of BCR-ABL gene in the blood, or none at all.

You’ll need to keep TK inhibitors for as long as they’re controlling the leukaemia.

Monitoring response to treatment

When you first start treatment with a TK inhibitor, you will need to go to the clinic every week or so. This is so your doctors can closely monitor how you’re responding to treatment, and so they can check for any side effects.

As time goes on, you won’t need to go to the clinic as often. Eventually you may only need a check-up every 2–3 months.

At these check-ups, your doctor will ask about your general health and whether you have had any new symptoms or side effects from treatment. You will usually have blood taken to check the numbers of blood cells (a full blood count) and for a PCR test. Sometimes you may also have a bone marrow sample taken. Your doctor can tell you how often this might be needed.

The results of these tests help your doctors know how well your leukaemia is responding to treatment, so they can make any changes if needed.

Levels of response

The aim of treatment is to put your CML into remission. Remission means there are no signs of CML in your blood. There are different levels of response, which we’ve listed below.

Haematological response

The white blood cell count in the blood is usually high when you first develop CML. If there is a haematological response, it means your full blood count has returned to normal and no leukaemia cells can be seen. If your spleen was larger than normal when you were first diagnosed, this should also have gone back to its normal size.

Most people get a haematological response within three months of starting imatinib.

Cytogenetic response

This is the next level of response. It refers to the amount of Philadelphia chromosome in the blood and bone marrow. As treatment begins to work, the number of Philadelphia chromosome-positive (Ph+) cells in the blood and bone marrow goes down.

To check for a cytogenetic response, you will have a bone marrow sample taken. Your doctors will usually examine at least 20 cells from the sample to see whether there has been a cytogenetic response. There are different levels of cytogenetic response – the level depends on the amount of Ph+ cells in the bone marrow.

It takes longer to get a cytogenetic response than a haematological response. It sometimes takes many months.

About 80% of (8 out of 10) people taking imatinib for CML in the chronic phase get a complete cytogenetic response. This means there are no Ph+ cells in the bone marrow.

Molecular response

Even after you have a cytogenetic response, there can still be leukaemia cells in your blood. Because there may only be one leukaemia cell among thousands of normal blood cells, a very sensitive test is needed to detect the leukaemia cells.

The PCR test can detect one leukaemia cell in up to 10,000 normal blood cells. It does this by measuring a substance made by the BCR-ABL gene in the leukaemia cells.

When you’re first diagnosed with CML, you’ll have blood taken for PCR testing. After diagnosis, you’ll have this done around every three months. Because it’s so sensitive, the PCR test may keep showing signs of leukaemia for many months after your treatment starts, even though you’re feeling well.

There are two different levels of molecular response:

  • A major molecular response is when there are tiny amounts of the BCR-ABL gene in the blood.
  • Molecularly undetectable leukaemia means the PCR test cannot detect any of the BCR-ABL gene in your blood.

Continuing to take treatment

You’ll usually keep taking the TK inhibitor for as long as it’s controlling your leukaemia. This is important even if your PCR tests don’t show any signs of leukaemia.

If you find it difficult to remember to take your tablets every day, you may find the following ideas helpful:

  • Take your tablets at the same time you usually do something else, for example when you eat your lunch or dinner.
  • Put your tablets in a place where you’ll see them every day.
  • Mark off each dose you take on a calendar, or use a seven-day pill container.
  • Keep a supply of tablets with you when you travel and take your medicine in your carry-on luggage when you fly.

Your prescriptions will be organised through the hospital, so you may have to go there to collect the tablets each time you need more. Tell your doctor, nurse or pharmacist if it is difficult for you to get to the hospital.

Back to Tyrosine kinase inhibitors explained

Side effects of TK inhibitors

Tyrosine Kinase Inhibitors (TKIs) can cause some side effects but these are usually mild and can be treated effectively.