Ovarian Cancer's 'PARP Inhibitor' — What Exactly Is This Drug, and Who Uses It?

When you are going through ovarian cancer treatment, at some point the words "PARP inhibitor" come out of your medical team's mouth. People hearing it for the first time usually make a certain face and ask, "Is that a chemotherapy drug? Or is it something else?" In truth, the name just looks a bit difficult; once you understand it, the way it works is quite intuitive. When DNA in our body's cells is damaged, the cells repair it on their own, and one of the workers that helps with this repair is an enzyme called PARP. A PARP inhibitor is, quite literally, a drug that ties this worker's hands.

So what is the benefit of tying that worker's hands? Here is where the gene called BRCA comes in. BRCA1 and BRCA2 are another repair crew that precisely splices DNA back together when it has been badly broken, and a considerable number of ovarian cancer patients carry a fault (mutation) in this gene. Because normal cells have intact BRCA, they can repair through another route even if PARP is blocked. But in a cancer cell whose BRCA is broken, once PARP is also blocked, every way to repair disappears completely. Both paths are cut off. In the end, the cancer cell collapses on its own while holding onto its damaged DNA. In technical terms this is called 'synthetic lethality,' meaning that the moment two weaknesses overlap, it becomes fatal.

That is why who uses this drug becomes important. When PARP inhibitors first appeared, they were used mainly only for people in whom a BRCA mutation had been confirmed. But as research accumulated, it became clear that even without BRCA specifically, tumors with a similar repair defect (a state known as HRD) can respond. So these days, they are often used as 'maintenance therapy' to delay recurrence after chemotherapy has sufficiently shrunk the tumor. One patient, after finishing first-line treatment, took this drug in pill form at a set time every day, and what she liked most was that she no longer had to go to the hospital every time for an injection.

Of course, it is not all good. The most common issues are nausea and fatigue. Once they actually start taking it, quite a few people lose their appetite or tire more easily than usual. Anemia or changes in platelet counts can also occur, so blood tests are done periodically during treatment. There are also complications that, though rare, deserve attention. So if you feel any symptom out of the ordinary while taking the drug, it is best not to endure it alone but to tell your medical team right away. In many cases, simply adjusting the dose or taking a short break makes things much more comfortable.

To sum up, a PARP inhibitor is a targeted therapy that precisely exploits the 'DNA-repair weakness' of ovarian cancer cells, and it suits especially well those who have a BRCA mutation or a similar defect. That is why the process of checking what characteristics your tumor has through genetic testing before starting treatment is becoming increasingly important. Whether you are a candidate for this drug, when to start, and how long to take it differ from person to person, so please use this article only to grasp the big picture, and be sure to discuss the specifics with your attending doctor.