When side effects are a good thing

It’s generally accepted in medical circles that there is no such thing as a cancer drug without side effects – at least, not a drug that actually works.  If a treatment has an effect on a biological process that has gone awry, then it will also affect healthy cells in the body, causing side effects.

This is certainly the case with current cancer treatments, and the side effects can be gruelling.  But now our scientists have found that – at least in the case of breast cancer – side effects may sometimes have a positive side.

Oestrogen and breast cancer
A large proportion of breast cancers are fuelled by the female sex hormone oestrogen.  For a number of years doctors have used highly effective drugs that block the production of oestrogen (such as anastrozole), or its ability to act on tumours (such as tamoxifen). These drugs have made a significant contribution to the impressive survival rates we see for breast cancer today.

But oestrogen also plays a host of other roles in the normal running of a woman’s body,  so blocking its production or activity can cause side effects.  These include hot flushes, night sweats and joint pain.

Now researchers led by Cancer Research UK ‘s Professor Jack Cuzick have found that these side effects are actually a good sign that the treatment is working.

“No pain, no gain”
The scientists analysed data from a trial called ATAC , which compared tamoxifen with anastrozole for post-menopausal women with breast cancer.  The study showed that although both drugs can effectively treat the disease, the cancer was around 25% less likely to return in those who had taken anastrozole.

In this new research, published in the journal Lancet Oncology, the scientists looked at around 2,000 women taking each drug, and noted those who had hot flushes or joint pain within three months of starting the trial.

They found that women with hot flushes were 16 per cent less likely to have a recurrence.  Those with joint pain were 40 per cent less likely to have the cancer come back, while the lowest rates of recurrence were seen in women with both side effects.

So what does this mean?
For a start, it shows that side effects can be a good indication that treatment is working – at least in this situation.  And that women who experience them should be encouraged to stick with the treatment, rather than stopping medication. But there are a few other things to bear in mind.

Firstly, this finding does not show that women who don’t experience side effects will not get any benefit from their treatment.

Less than half of the patients in the ATAC trial had hot flushes on either drug, while between 20 and 30 per cent had joint pain. But both drugs are highly effective in the majority of patients – the cancer came back in only 12 per cent of women on anastrozole, and 16 per cent on tamoxifen.

So this tells us that if you don’t have side effects from treatment, your chances of avoiding recurrence are very good.  But if you do have them, your chances are even better.

It’s also important to point out that the side effects experienced by the women were relatively mild, if somewhat unpleasant.  If a woman has very severe side effects following treatment for breast cancer, then she may be switched to a different treatment by her doctor.

Finally, the research raises the question of why some women have side effects (and why this is linked to their outcome), and why others don’t.  The answer is likely to boil down to genetic differences.

We’re already making progress in understanding the genetic “signatures” of tumours, and how these relate to survival (for example, this paper).  This new research tells us that investigating how side effects are linked to a person’s genetic makeup will also shed light on the effectiveness of treatment.  It means more work for our scientists, but big benefits for people with cancer.

Kat