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Mutations in Lynch syndrome genes MSH6 and PMS2 are associated with breast cancer


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Checked Other mutations: MSH6 or PMS2

Checked Special populations: Individuals with Lynch syndrome, MSH6 or PMS2 carriers

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A research study published in Genetics in Medicine earlier this year shows that women with mutations in MSH6 and PMS2, two Lynch syndrome genes, have a modest (2 to 3-fold) but significantly increased risk for breast cancer. Lynch syndrome mutations have a known risk of colorectal, ovarian and uterine/endometrial cancer, as well as many other cancers. This is the first study to evaluate breast cancer risk in women with mutations in specific Lynch syndrome genes. (6/14/18)

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STUDY AT A GLANCE

This study is about:

The risk of breast cancer associated with Lynch syndrome gene mutations.

Why is this study important?

This study is the first to address gene-specific breast cancer risk for four Lynch syndrome genes in a single group of women. Significantly, 11.1% of women with a LS mutation had no personal or family history of colorectal, endometrial or ovarian cancer.

Study background:

Lynch syndrome (LS), also known as hereditary non-polyposis colorectal cancer (HNPCC), is a hereditary cancer syndrome. LS is associated with multiple types of cancers, particularly colon, ovarian and endometrial/uterine cancer.

LS is caused by inherited mutations in MLH1, MSH2, MSH6, PMS2 or particular mutations in the related EPCAM gene. Previous studies have found mixed results on the association between LS and breast cancer risk. However, these studies were evaluating all Lynch genes combined while this study evaluates each gene separately.

Study findings: 

The researchers retrospectively identified 423 women who carried a mutation in one of 4 LS genes (MLH1, MSH2, MSH6 or PMS2).

  • MLH1 and MSH2 carriers did not have an increased risk of breast cancer.
  • MSH6 and PMS2 carriers had a modest but significantly increased risk of breast cancer compared to the general population:
    • MSH6 carriers had 2.11-fold more cases of breast cancer.
    • PMS2 carriers had 2.92-fold more cases of breast cancer.
  • The estimated cumulative incidence of breast cancer was significantly greater for MSH6 and PMS2 carriers:
    • MSH6 carriers: 31.1% predicted to have breast cancer by age 60.
    • PMS2 carriers: 37.7% predicted to have breast cancer by age 60.
  • 11.1% of women with a LS mutation had no personal or family history of colorectal, endometrial or ovarian cancer.

    • Families with MSH6 or PMS2 pathogenic variants report breast cancer most often. In contrast, families with MSH2 or MLH1 pathogenic variants report colorectal cancer most often.

What does this mean for me?

These observations suggest that women whose personal or family history is limited to breast cancer may carry MSH6 or PMS2 mutations. These mutations may be undetected if only the common breast cancer genes are examined.

If you have breast cancer and you have a personal or family history of colorectal, endometrial or ovarian cancer, genetic counseling and testing for LS gene mutations may be warranted.

If you have a family history of breast cancer and you do not have a mutation in a known breast cancer predisposing gene, you might have a mutation in an LS gene. Genetic counseling and testing for LS gene mutations may be warranted.

If you have a mutation in MSH6 or PMS2 genes, you have increased risk endometrial, ovarian colorectal and other cancers. The possible increased risk of breast cancer found in this study should be discussed with your health care provider. Additional studies to confirm the risk for breast cancer are needed.  Currently, the National Comprehensive Cancer Network (NCCN) Guidelines for breast surveillance for people with LS are based on family history and do not include increased surveillance based on a LS gene mutation alone. Screening for other Lynch syndrome-related cancers is warranted. For additional information regarding management guidelines for Lynch syndrome, visit our information page on LS.

Questions to ask your health care provider

  • Should I consider genetic counseling or genetic testing for Lynch syndrome mutations given my personal and family history?
  • My family has a history of Lynch syndrome, should I consider genetic counseling and testing?
  • As a Lynch syndrome mutation carrier, what breast cancer screening options should I consider? What are my risks for other cancers?
  • As a Lynch syndrome mutation carrier, what preventive measures should I consider?
  • Can you refer me to a genetics expert?

IN-DEPTH REVIEW OF RESEARCH

Study background:

Lynch syndrome (LS) is an inherited cancer syndrome also known as hereditary non-polyposis colorectal cancer (HNPCC). It is associated with multiple types of cancers, particularly colon and endometrial/uterine cancer. LS accounts for 3-5% of all colorectal cases annually. LS occurs in people with mutations in genes of the mismatch repair system. These genes include MLH1, MSH2, MSH6, PMS2 genes and related EPCAM gene. LS gene mutations are not uncommon. About 1 in 440 people carry a mutation in a LS gene.

Past studies grouped all of the LS genes together to evaluate the cancer incidence. A 2013 review found that 13 studies showed no association between LS genes and breast cancer while 8 studies found an increased risk of breast cancer among LS carriers. In this study, researchers wanted to clarify whether each of the LS genes was or was not associated with breast cancer.

Researchers of this study wanted to know:

The risk of breast cancer among women who carry a mutation in one of the Lynch syndrome genes: MLH1, MSH2, MSH6 or PMS2.

Populations looked at in this study:

The researchers retrospectively identified 423 women from over 50,000 women who had multigene hereditary cancer panel testing at GeneDx between 2013 and 2016. These women carried a mutation in one of 4 genes (MLH1, MSH2, MSH6 or PMS2). They were at least 18 years old and were diagnosed with invasive breast cancer or ductal carcinoma in situ. Researchers limited their study to women carrying mutations that were classified as pathogenic or likely pathogenic according to 2015 guidelines by the American College of Medical Genetics and Genomics/Association for Molecular Pathology. They collected demographic information, clinical history and family history from genetic test requests.

Study findings:  

Breast cancer was not uncommon among these LS carriers.

  • 25.3% of women with a LS mutation had a history of breast cancer; 1.4% had more than one primary breast cancer.
  • Average age at first breast cancer diagnosis was 50.

Breast cancer occurred in women with a pathogenic mutation in MSH6 or PMS2 in the absence of other LS associated cancers:

  • 18.6 % of MSH6 carriers had breast cancer only.
  • 29.0% with PMS2 carriers had breast cancer only.

Families with MSH6 or PMS2 pathogenic variants report breast cancer most often. In contrast, families with MSH2 or MLH1 pathogenic variants report colorectal cancer most often.

  • 11.1% of women with a LS mutation had no personal or family history of colorectal, endometrial or ovarian cancer.

To determine the risk of breast cancer for these carriers, researchers compared the number of women with breast cancer to the number of women they expected would have breast cancer based on incidence in the general population (using the national SEER cancer registry data).

  • MLH1 and MSH2 carriers did not have an increased risk of breast cancer.
  • MSH6 and PMS2 carriers had a modest, but significantly increased, risk of breast cancer as compared to the general population:
    • MSH6 carriers had 2.11-fold more cases of breast cancer.
    • PMS2 carriers had 2.92-fold more cases of breast cancer.
  • The estimated cumulative incidence of breast cancer was significantly greater for PMS2 and MSH6 carriers.
    • PMS2 carriers: 37.7 % predicted to have breast cancer by age 60.
    • MSH6 carriers: 31.1 % predicted to have breast cancer by age 60.
    • MSH2 carriers: 16.1 % predicted to have breast cancer by age 60.
    • MLH1 carriers: 15.5 % predicted to have breast cancer by age 60.

These observations suggest that women whose personal or family history is limited to breast cancer may carry MSH6 or PMS2 mutations. These mutations may be undetected if only the common breast cancer genes are examined.

As expected, women with pathogenic mutations in a Lynch syndrome gene had higher risks of other cancers than the general population: colorectal cancer was 3 to 19-fold higher, endometrial cancer was 7 to 18-fold higher, and ovarian cancer was 3 to 12-fold higher.

Researchers wanted to know which genetic testing criteria would best detect LS mutations prospectively. They examined the personal and family histories of these women with known LS mutations retrospectively. They applied three established clinical or testing criteria (Amsterdam II and Revised Bethesda guidelines for Lynch syndrome and NCCN BRCA1/2 testing guidelines). Women with pathogenic mutations in an LS gene met NCCN BRCA1/2 guidelines for genetic testing more often (58% of the time) than the other two testing criteria (23, 24% of the time). They concluded that genetic test criteria should be continuously reevaluated.

Limitations:

Women in this study were retrospectively selected because they had genetic testing that identified a mutation in one of the Lynch syndrome genes. The decision to have genetic testing may reflect an individual’s personal and family cancer history, therefore this group of women may not be representative of all LS carriers.

Researchers had access only to clinical information provided at the time of genetic testing request; information about subsequent cancers was unknown.

Researchers acknowledge that the demographic makeup of the women in this study may not be racially or ethnically representative.

Lastly, researchers acknowledge that cumulative survival time is difficult to determine with a retrospective study. For these reasons, the study limited estimation of breast cancer incidence to age 60. Further prospective testing of potential Lynch syndrome mutation carriers will help clarify these issues.

Conclusions:

Women with mutations in MSH6 and PMS2 have an 2-3-fold increased risk of breast cancer compared to the general population and have increased risk for other cancers associated with Lynch syndrome. Women with a personal or family history of breast cancer may want to consider multigene panel testing that includes the LS genes (especially MSH6 and PMS2).

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Posted 6/14/18

References

Roberts ME, Jackson SA, Susswein LR, et al. "MSH6 and PMS2 germ-line pathogenic variants implicated in Lynch syndrome are associated with breast cancer." Genetics in Medicine. Jan. 18, 2018. doi: 10.1038/gim.2017.254.

ten Broeke SW, Suerink M, Nielsen M, "Response to Roberts et al. 2018: Is breast cancer truly caused by MSH6 and PMS2 variants or is it simply due to a high prevalence of these variants in the population?" Genetics in Medicine. May 24, 2018. doi: 10.1038/s41436-018-0029-1.

Roberts ME, Zeinomar N, Solomon BD, et al. "Response to ten Broeke et al." Genetics in Medicine. May 24, 2018. doi:10.1038/s41436-018-0031-7 

Win AK, Lindor NM, Jenkins MA. "Risk of breast cancer in Lynch syndrome: a systematic review." 2013.15(2):R27.

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