The researches find that the cancer treatments can work in lots of different ways, aiming to kill tumor cells or keep them under control. Ideally they cause tumors to shrink, but drugs can also be considered successful if they stop tumors growing. But unfortunately, the effects don’t always last forever. Sometimes a drug can have an initial effect on a cancer’s size or growth; but then the tumor starts to grow again despite treatment. This is what’s known as drug resistance.

The cancer treatments

“No matter what amazing new treatments we come up with; eventually at least some patients’ tumors will become resistant to them, that is the reality,” says Dr. Georgina Sava, a research associate working on drug resistance in breast cancer in Professor Simak Ali’s lab at Imperial College London. Sava tries to predict ways that resistance may develop to new drugs; aiming to stay one step ahead of the cancer. She says drug resistance is a big problem in cancer and there are lots of people working to understand how and why it happens.

Resistance comes about because of faults in the DNA of cancer cells. We’ve blogged before about how cells first become cancerous. And it turns out the same processes can help a cancer evolve and adapt to treatments. Some of the changes that arise can mean cells stop responding to cancer drugs like chemotherapy; targeted cancer drugs or hormone therapy. Cancer cells develop from normal cells because of a build up of mistakes in key parts of our DNA. But it doesn’t stop there. Even when a cell has become cancerous; DNA faults continue to appear. Some of these faults can make the cells resistant to a treatment.

DNA faults continue to appear

Individual cells in a tumor can have different DNA faults and, as a result, not every cancer cell in a tumor is exactly the same. This is where problems arise. “When cancer cells are treated with a drug, it’s like survival of the fittest,” says Sava. “in an ideal situation, every cell in a tumor would be killed. But, if even a single cell happens to be resistant to the drug, it will survive and eventually grow to become a new tumor.” There are lots of ways that cancer cells can become resistant to a drug. Sava highlighted the problem of resistance to hormone therapies, which are used to treat some breast cancers that are driven by the hormone estrogen.