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PubMed This is a summary of 21 peer-reviewed journal articles Updated
Oncology · Hereditary Breast and Ovarian Cancer Syndrome

Targeted Treatments and PARP Inhibitors

At a Glance

PARP inhibitors are targeted daily medications that exploit the genetic weakness of BRCA-mutated cancers. By blocking the cancer cell's backup DNA repair process, these drugs cause the cancer cells to die, offering an effective, precise treatment for hereditary cancers.

When a cancer diagnosis occurs in the context of HBOC, the very genetic “flaw” that increased the risk of cancer—the inability to repair DNA correctly—becomes the cancer’s greatest weakness. Modern medicine uses targeted therapies to exploit this vulnerability, offering options that are often more precise than traditional chemotherapy [1][2].

The Concept of Synthetic Lethality

To understand how these treatments work, imagine a table with four legs. If one leg is broken (a BRCA mutation), the table can still stand on the other three. However, if you purposely break one more specific leg, the whole table collapses. This is synthetic lethality [1][3].

In your body, cells use multiple pathways to fix DNA damage.

  1. HR Pathway: BRCA1 and BRCA2 are the primary “workers” in this pathway. In HBOC-associated cancers, this pathway is broken (HRD) [4][5].
  2. PARP Pathway: This is a backup pathway that fixes smaller, single-strand breaks in DNA [1][6].

PARP inhibitors are drugs that shut down that backup pathway. In a healthy cell, this is fine because the BRCA “workers” can still fix the damage. But in a cancer cell where the BRCA pathway is already broken, shutting down PARP leaves the cell with no way to repair itself, causing the cancer cell to die [1][3][7].

FDA-Approved PARP Inhibitors

Several PARP inhibitors are currently used to treat cancers associated with BRCA mutations and HRD. They are often taken as a daily pill [8].

  • Olaparib (Lynparza): Approved for certain types of breast, ovarian, prostate, and pancreatic cancers [8][9][10].
  • Niraparib (Zejula): Frequently used as “maintenance” therapy for ovarian cancer to help keep the cancer from coming back after chemotherapy [11][8].
  • Rucaparib (Rubraca): Approved for specific types of ovarian and prostate cancers [8][12].
  • Talazoparib (Talzenna): Used primarily for advanced breast cancer with a germline BRCA mutation [8][13].

The Role of Platinum Chemotherapy

Before PARP inhibitors were available, doctors noticed that BRCA-mutated cancers responded exceptionally well to platinum-based chemotherapies (like carboplatin or cisplatin) [14][15].

These drugs work by flooding the cancer cells with DNA damage. Because the cells lack the BRCA “repair kit,” they cannot survive the onslaught [14][16]. Today, platinum chemotherapy is often used first to shrink the tumor, sometimes followed by a PARP inhibitor to maintain the results [17][18].

Understanding Resistance

While these treatments are often very effective, cancer cells are “smart” and can sometimes find ways to survive.

  • Reversion Mutations: In some cases, the cancer cells actually “fix” their own BRCA mutation, regaining the ability to repair DNA and becoming resistant to PARP inhibitors and platinum drugs [19][20].
  • Stabilization: Cells may find other ways to protect their DNA during replication, bypassing the need for the broken repair pathways [21][20].

If resistance occurs, your doctor may use specialized blood tests (like ctDNA or “liquid biopsies”) to see if these changes have happened, which helps them decide on the next best treatment [19].

Common questions in this guide

What are PARP inhibitors and how do they work?
PARP inhibitors are targeted cancer drugs that block a specific DNA repair pathway in cells. In cancers with BRCA mutations, shutting down this backup repair system leaves the cancer cells unable to survive, a process known as synthetic lethality.
What does HRD mean for my cancer treatment?
Homologous Recombination Deficiency (HRD) means your cancer cells are unable to repair their DNA normally due to a broken pathway. If your tumor shows HRD, it indicates that your cancer may be highly vulnerable to targeted treatments like PARP inhibitors.
Why is platinum chemotherapy used for BRCA-mutated cancers?
Platinum chemotherapy works by heavily damaging the DNA of cancer cells. Because cancers associated with BRCA mutations lack the necessary 'repair kit' to fix this damage, they are often unable to survive these types of drugs.
Which PARP inhibitors are approved for BRCA-related cancers?
Several PARP inhibitors are currently FDA-approved, including Olaparib, Niraparib, Rucaparib, and Talazoparib. Your oncologist will recommend the most appropriate option based on your specific type of cancer and whether it is being used for active treatment or maintenance therapy.
What happens if my cancer stops responding to a PARP inhibitor?
Cancer cells can sometimes develop 'reversion mutations' that fix their broken DNA repair pathways, making the PARP inhibitor less effective. Your doctor can use specialized blood tests, called liquid biopsies, to check for these changes and determine your next best treatment step.

Questions for Your Doctor

5 questions

  • •Does my tumor show 'Homologous Recombination Deficiency' (HRD), and does that make me a candidate for a PARP inhibitor?
  • •If I am already on platinum chemotherapy, would I benefit from switching to a PARP inhibitor for maintenance therapy afterward?
  • •Which specific PARP inhibitor (Olaparib, Niraparib, etc.) is most appropriate for my type of cancer and its genetic profile?
  • •How will we monitor my blood counts while I am taking these medications?
  • •If my cancer stops responding to a PARP inhibitor, are there tests to see if my cells have developed 'reversion mutations'?

Questions for You

3 questions

  • •How did my body respond to platinum-based chemotherapy in the past? Did I have significant side effects?
  • •Am I prepared for the potential side effects of PARP inhibitors, such as fatigue or nausea, and do I have a support system to help manage them?
  • •Is the convenience of an oral pill (PARP inhibitor) a high priority for me compared to intravenous chemotherapy?

References

References (21)
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This page provides educational information about targeted therapies and PARP inhibitors for HBOC. Always consult your oncologist to determine the most appropriate treatment plan for your specific genetic profile and cancer diagnosis.

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