Researchers studied cancer patients taking a drug called olaparib to see if it causes low folate levels (a B vitamin your body needs). They found that nearly all patients developed low folate within a few weeks of starting the drug, though this didn’t always cause serious anemia (low red blood cells). When patients took folic acid supplements, their folate levels improved. The study was small with only 9 patients, but it suggests doctors should check folate levels in cancer patients taking olaparib and consider giving them supplements if levels drop.

The Quick Take

  • What they studied: Does a cancer drug called olaparib cause patients to lose folate (a B vitamin), and does taking folic acid supplements help fix this problem?
  • Who participated: Nine cancer patients (mostly with ovarian or breast cancer) who were taking olaparib and developed low folate levels and mild anemia
  • Key finding: Nearly all 9 patients (8 out of 9) developed low folate levels within 3 months of starting olaparib. Seven patients also developed mild anemia. When given folic acid supplements, their folate levels improved.
  • What it means for you: If you’re taking olaparib for cancer, your doctor may want to check your folate levels regularly and consider giving you folic acid supplements. This is still preliminary evidence from a very small study, so talk to your doctor about whether this applies to you.

The Research Details

This was a prospective study, meaning researchers followed patients forward in time as they took olaparib to see what happened. Patients with solid tumors (cancers that form lumps) who were starting olaparib treatment were enrolled. Researchers measured their folate levels (a B vitamin) and hemoglobin levels (which shows how many red blood cells you have) at the beginning and throughout treatment. Some patients who developed both low folate and mild anemia were randomly assigned to either receive folic acid supplements or a placebo (fake pill) to see if supplements helped. The study tracked how often folate deficiency occurred, when it happened, and whether supplements could fix it.

Previous research suggested olaparib might cause folate deficiency and anemia, but that was based on looking back at patient records. This prospective approach is better because researchers watched patients carefully from the start, measuring folate levels regularly. This helps doctors understand exactly when and how often this side effect happens, which is important for knowing when to check for it and treat it.

This study is small (only 9 patients), which limits how much we can trust the results. Not all patients completed the randomized part of the study as planned—only 4 out of 9 were actually randomized to receive either supplements or placebo. The study was open-label, meaning both patients and doctors knew who was getting supplements, which could affect results. However, the consistent finding that nearly all patients developed low folate is noteworthy and suggests this is a real effect worth monitoring.

What the Results Show

All nine patients showed decreased folate levels after starting olaparib, with eight developing low folate within 3 months. This happened quickly—most within the first few weeks of treatment. Seven of the nine patients also developed mild anemia (grade 1, meaning hemoglobin below 12.0 g/dL). However, the researchers found that low folate levels didn’t always cause serious anemia problems. When patients received folic acid supplements, their folate levels returned to normal. When patients stopped taking olaparib, their folate levels also improved naturally. Three patients withdrew from the study due to disease progression, but this didn’t appear to be related to the folate deficiency.

The study tracked whether patients needed blood transfusions, had to pause their cancer treatment, reduce their dose, or stop the drug entirely. While the abstract doesn’t provide detailed numbers on these outcomes, the overall pattern suggests that while folate deficiency was common, it didn’t cause severe enough problems to force most patients to stop their cancer treatment. This is important because it means the folate deficiency, while common, may not be a major barrier to continuing olaparib therapy if properly managed with supplements.

A previous study looking back at patient records found that 87.5% of patients developed both folate deficiency and anemia together. This new prospective study found similar rates of folate deficiency (nearly 100%) but found that the anemia wasn’t always clinically significant (serious enough to cause problems). This suggests that while olaparib definitely causes folate deficiency, the connection to serious anemia may be weaker than previously thought. The new study provides more detailed timing information, showing that folate drops quickly—within weeks rather than months.

The study is very small with only 9 patients, making it hard to apply results to larger populations. Only 4 patients actually completed the randomized supplement portion, which weakens conclusions about whether supplements help. The study was open-label, meaning patients and doctors knew who was getting supplements, which could create bias. Three patients dropped out due to disease progression, reducing the final sample size. The study didn’t track long-term outcomes or compare different supplement doses. These limitations mean we should view the results as preliminary evidence that warrants larger, more rigorous studies.

The Bottom Line

If you’re taking olaparib for cancer, ask your doctor to check your folate levels regularly (especially within the first 3 months). If your folate levels drop, taking folic acid supplements appears to help restore them. This recommendation has moderate confidence because it comes from a small study, but the consistent findings across all patients suggest it’s worth monitoring. Discuss with your oncologist whether routine folate monitoring and supplementation should be part of your treatment plan.

This research is most relevant to cancer patients (particularly those with ovarian or breast cancer) who are taking or considering olaparib. It’s also important for oncologists and cancer care teams who prescribe this drug. If you have a history of anemia or folate deficiency, this is especially relevant to discuss with your doctor. This doesn’t apply to people not taking olaparib or those with other types of cancer not mentioned in the study.

Folate deficiency appears to develop quickly—within 3 months for most patients, often within weeks. If you start folic acid supplements, folate levels should improve within weeks. However, you may need ongoing monitoring throughout your olaparib treatment since the deficiency appears to be a consistent side effect of the drug rather than a temporary problem.

Want to Apply This Research?

  • Track your folate supplement intake (dose and frequency) and note any symptoms of anemia like unusual fatigue, shortness of breath, or dizziness. Record these weekly in your health app to share with your doctor at appointments.
  • If your doctor prescribes folic acid supplements alongside olaparib, set a daily reminder in your app to take them at the same time each day (such as with breakfast). Create a simple checklist to mark off each day you take your supplement to ensure consistency.
  • Schedule folate level blood tests every 4-6 weeks during the first 3 months of olaparib treatment, then every 8-12 weeks if stable. Log the results in your app and track any symptoms of anemia. Share this data with your oncology team to adjust supplementation as needed.

This research is preliminary and based on a very small study of only 9 patients. The findings should not be used to make medical decisions without consulting your oncologist. If you are taking olaparib or considering this treatment, discuss folate monitoring and supplementation with your cancer care team. This information is educational and not a substitute for professional medical advice, diagnosis, or treatment. Always follow your doctor’s recommendations for your specific situation.