How PARP Inhibitors Affect Your Blood

The American Society of Clinical Oncology (ASCO) guidelines recommend PARP inhibitors be offered to women, with or without genetic mutations, who are newly diagnosed with stage III or IV ovarian cancer and have improved with chemotherapy.

But these drugs, though given in pill form rather than through an IV infusion, have significant side effects like other medications used to treat ovarian cancer. Just as doctors can manage many of traditional chemo side effects nausea, for instance they have devised ways to help women cope with the side effects of PARP inhibitor treatment. One common side effects of PARP inhibitor treatment is fatigue, and that can be a result of anemia.

PARP inhibitors' effects on the blood are among the most concerning to doctors. These drugs disrupt how cells repair damaged DNA, killing off tumor cells, but also some healthy cells as well. Bone marrow activity may be affected, which is why healthy blood counts–red blood cells, white blood cells, and platelets may be diminished.

Hematologic (blood-related) side effects can include:

• Anemia (a drop in the red blood cells), which may result in fatigue
• Thrombocytopenia (a drop in the platelet count), which can cause easy bruising and excessive bleeding
• Neutropenia (a drop in the white blood cell count), which can leave people more susceptible to infection

Dealing with these side effects is dependent on patients and their doctors working together to devise the best strategy, says Dr. Ramez Eskander, gynecologic oncologist at the University of California, San Diego. One of the most important steps is for doctors to frequently monitor their patients' blood counts and check the lab results regularly.

"Some PARP inhibitors require more frequent assessments," says Dr. Eskander.

The Importance of Lab Tests

With niraparib, doctors talk about "weights and plates." In other words, assessing how much a patient weighs along with their platelet count to make sure the numbers are in balance. "So if a patient weighs less than 77 kilograms (170 pounds) or has a platelet count less than 150,000, we should start a lower dose of the drug," he explains.

Once treatment has begun, doctors assess the lab results to determine whether to lower the dose of the PARP inhibitor or stop the treatment temporarily to allow the blood counts to build themselves up.

For instance, if a patient develops anemia, "we interrupt the treatment, which is perfectly acceptable," he says. "And when we recheck labs, if the lab counts are good again we can resume treatment at a lower dose or at the same dose as previously and see how patients are doing."

Managing PARP inhibitor side effects including the effects on blood is a dynamic, interactive process individualized to each woman. With proper monitoring and dose adjustment, and a good doctor-patient partnership, the blood-related side effects of PARP inhibitors can be handled and treatment can be continued.

"It’s about education to empower our patients. It’s about communication, so that our patients feel confident in being able to reach out to us. And it’s about strategies to manage those side effects when patients experience them,” says Dr. Eskander.

Dr. Amanika Kumar of the Mayo Clinic who spoke to SurvivorNet, cautioned that women still need to speak with their doctor to evaluate the benefit of taking a PARP inhibitor to extend life, because there are very real side effects due to the toxicity of the drug.

"Patients with HRD (homologous recombination deficiency) have a far better response than those without and those with BRCA mutations even more so. It is on us as clinicians to help patients understand the risks and benefits of treatment. Patients that have no mutation or HRD may choose not to go on maintenance (in fact I recommend they don't) because there is real toxicity to these meds."

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