Study: Risk of peritoneal cancer is low for people with an inherited BRCA mutation after surgery

Relevance: Medium-High

Strength of Science: Medium-High

Research Timeline: Post Approval

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What is this study about?

Researchers wanted to understand the risk of peritoneal cancer among women with a BRCA1 or BRCA2 mutation who had preventive surgery that removed both ovaries (bilateral oophorectomy).

What is peritoneal cancer?

Peritoneal cancer is a rare cancer that looks and acts similarly to ovarian and fallopian tube cancer. It begins from the lining the cavity of the abdomen and covering the abdominal organs.

All three cancers (ovarian, fallopian tube and peritoneal):

• affect the reproductive system.
• look the same under a microscope.
• are treated similarly. 

Due to these similarities, many professional medical organizations group peritoneal cancer with ovarian and fallopian tube cancers.

Risk factors for ovarian, fallopian and peritoneal cancers include a family history of breast and/or ovarian cancer and inheriting a mutation in a high-risk gene, such as BRCA1 or BRCA2.

Why is this study important?

Until recently, experts believed that ovarian, fallopian tube and peritoneal cancers had separate origins. Now, however, they believe that most of these cancers begin in fallopian tubes. Cancer or precancerous cells are thought to move from the fallopian tubes to the ovaries and the lining of the abdomen (the peritoneum), resulting in ovarian and peritoneal cancer. For this reason, removing the fallopian tubes (salpingectomy) at the same time as risk-reducing removal of the ovaries (oophorectomy) is now recommended for people with an inherited BRCA1 or BRCA2 mutation. This combined surgery is called risk-reducing bilateral salpingo-oophorectomy (RRSO).

Even after RRSO, some women develop peritoneal cancer. Researchers wanted to understand if these peritoneal cancers started in the lining of the abdomen or were caused by microscopic fallopian tube cancer cells that escaped into the abdomen before these women had surgery.  

To better understand the risk of peritoneal cancer among women who have an inherited mutation in BRCA1 or BRCA2 and had risk-reducing removal of their ovaries, researchers studied how frequently peritoneal cancer occurred among this group. Studying BRCA mutation carriers who have had risk-reducing surgery will also give insight into where peritoneal cancer begins.

Study findings

This study included 6,310 women with a BRCA1 or BRCA2 mutation who had both ovaries removed (bilateral oophorectomy). Women were monitored for almost eight years at 83 clinics in 12 countries.

During this time, 55 women developed peritoneal cancer:

• 45 had an inherited mutation in BRCA1.
• 8 had an inherited mutation in BRCA2.
• 2 had an inherited mutation in BRCA1 and BRCA2.

Most people who developed peritoneal cancer after removal of both ovaries also had their fallopian tubes removed:

• 48 had their fallopian tubes removed at the time of their risk-reducing oophorectomy.
• 3 did not have their fallopian tubes removed.
• It is not known whether the remaining 4 people who developed peritoneal cancer had their fallopian tubes removed.

Risk of Peritoneal Cancer

Researchers were able to calculate the yearly risk of peritoneal cancer after risk-reducing surgery. The risk of peritoneal cancer was:

• 0.14 percent for BRCA1 mutation carriers.
• 0.06 percent for BRCA2 mutation carriers.

Researchers also calculated the risk of developing peritoneal cancer 20 years after risk-reducing surgery. The 20-year risk of peritoneal cancer was:

• 2.7 percent for BRCA1 mutation carriers.
• 0.9 percent for BRCA2 mutation carriers.

There were no peritoneal cancers in BRCA1 mutation carriers who had risk-reducing surgery before age 35. Similarly, there were no peritoneal cancers in BRCA2 mutation carriers who had risk-reducing surgery before age 45.

There was a sharp decrease in peritoneal cancers among women who had oophorectomy after 2005. An increased effort has been made henceforth to ensure that both ovaries and fallopian tubes are removed at the time of risk-reducing surgery. This decrease in peritoneal cancer among mutation carriers supports the idea that peritoneal cancer, like ovarian cancer, begins in the fallopian tubes.

What does this mean for me?

These results support the current recommendation that RRSO should be performed by age 35-40 for BRCA1 mutation carriers and before age 45 for BRCA2 mutation carriers. The remaining risk of peritoneal cancer after RRSO has been decreasing over the last 20 years and is now very small, likely due to inclusion of salpingectomy as part of standard of care for RRSO surgeries.

Reference

Narod SA, Gronwald J, Karlan B, et al. Incidence of peritoneal cancer after oophorectomy among BRCA1 and BRCA2 mutation carriers. Journal of the National Cancer Institute. 2024. 116(11):1753-1760.

Disclosure: FORCE receives funding from industry sponsors, including companies that manufacture cancer drugs, tests and devices. All XRAYS articles are written independently of any sponsor and are reviewed by members of our Scientific Advisory Board prior to publication to assure scientific integrity.

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posted 1/23/25