We’ve done our best to round up some key facts that will help to demystify targeted therapies and the science behind them.

If your doctor has recommended that you start a course of targeted cancer therapy, you might have a lot of questions. How is it different to chemotherapy, radiotherapy or other kinds of cancer treatment? Are targeted therapy side effects better or worse? How exactly can a drug “target” the cancer?

What is molecular targeted therapy?

targeted therapy for breast cancer

Understanding exactly how targeted cancer therapy works takes a little biology knowledge, so first, let’s get back to basics.

Every cell has a ‘control centre’ called the nucleus, which sends signals to the rest of the cell telling it what to do; divide, stop dividing, die off – that sort of thing.

Cancer happens when your cells malfunction. Instead of sending all those normal healthy signals that help your body to grow healthy tissue and function as it should, the nucleus begins to send abnormal signals, causing the cell to divide at a higher rate than usual. These cells keep on dividing and giving out abnormal signals until they form a big lump of cells, which we call a tumour. 

Eventually, a tumour may grow large enough that it develops its own blood supply, keeping the abnormal cells supplied with all the elements they need to carry on multiplying.

Targeted cancer therapy uses this knowledge of how cancer cells work to try and fight it in the most efficient way possible.

Other treatments such as chemotherapy and radiotherapy cause a more general damaging effect to cells in the affected area, both cancerous and non-cancerous. But the idea with targeted therapies is to prevent growth or even cause shrinkage of cancerous cells and tumours, whilst leaving as many normal cells intact as possible. So if chemo is a machine gun, targeted therapies are like a team of highly-trained snipers.

How does targeted cancer therapy work?

targeted therapy drugs

Targeted therapies for lung cancer, breast cancer and bladder cancers will all involve different scientific mechanisms. Each type of cancer has its own vulnerabilities, and different drugs can target those in ways that are most suited to the area of your body where the cancer is located. However, across the group of targeted cancer therapies, there are four main ways of tackling the tumour.

Cutting off blood supply

targeted therapy for lung cancer

Earlier we mentioned how tumours can sometimes develop their own blood supply, which keeps bringing “supplies” to the cancer cells and enables them to continue growing and dividing. One method of attacking the tumour, then, is to cut off this blood supply.

The drugs that achieve this are called ‘angiogenesis inhibitors’. Think of it like a siege – when the enemy’s food and supplies are cut off, it’s only a matter of time until they run out of energy and begins to surrender. When angiogenesis inhibitors work, cancerous cells are unable to continue multiplying and eventually begin dying off, resulting in shrinkage of the tumour.

Blocking cancer cell signals

targeted cancer treatment

If cancer is caused by cells getting the wrong kind of signals, wouldn’t it be good if we could just… turn the signals off? Well, with targeted therapies, sometimes we can. “Cancer growth inhibitors” float around the bloodstream looking for cancerous cells, and when they find them, they either stick to the outside of the cell, or burrow their way inside. Once they’re “in position,” these molecules block the signals within the cancer cell that are telling it to divide, effectively slowing down or even stopping the growth of the tumour.

Stimulating the immune system

cancer growth inhibitors

Your body already comes with its own set of defences against disease – though it may be weakened by cancer and its treatment, your immune system can still help to tackle some kinds of cancerous cells. Targeted therapies such as “monoclonal antibodies” and vaccines take advantage of what your body already has, giving it a boost in the right direction and helping it to recognise which cells it should be attacking and destroying.

Delivering toxic substances

targeted cancer drugs

Finally, targeted therapies can work as simply as delivering a toxic substance to the cancerous cells in question, killing or damaging them to shrink the tumour and prevent it spreading. The difference between these drugs and other more “blanket” drugs such as chemotherapy is that these are able to deliver the toxic substances to a more specifically targeted type of cell, leaving more normal cells intact and healthy.

How is targeted cancer therapy given?

targeted cancer therapy drip

If your doctor has suggested you begin a course of targeted therapy, they will be able to give you all the specific details for your type. Just like each antibiotic only works for certain infections, targeted therapies have to be correctly matched in order to hit the right molecular target. The drugs might be given to you as a tablet, a subcutaneous injection (under the surface of the skin), or as an intravenous drip. If you have to have multiple treatments, you might be fitted with a catheter, a port, or a PICC line for easier access to your veins.

What are the most common targeted therapy side effects?

targeted therapy side effects

Though they were initially developed as a less toxic alternative to chemotherapy, these treatments can still come with some pretty heavy side effects. The most common side effects of targeted cancer therapies include diarrhoea and liver problems, though the side effect profile varies widely depending on which drug you’re being given, and what type of cancer it’s treating.

Other side effects experienced by people on targeted therapies include dry skin, acne, hair depigmentation and nail changes, as well as high blood pressure and occasionally problems with blood clotting. If you’re planning to get targeted therapy, your doctor should be able to advise you on the most common side effects specific to the drug you’ll be given.