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Researchers study the potential association between thyroid and breast cancers


This research is relevant for:

Checked Breast cancer survivors

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Checked Special populations: People with thyroid cancer and breast cancer

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Researchers and health care providers have observed that thyroid and breast cancers occur in the same patients more often than would be expected by chance. This has prompted them to attempt to better understand whether or not an association exists between the two cancers. This study found that compared to the average person, women diagnosed with breast cancer appear have a slightly higher risk for a diagnosis of thyroid cancer, and that women with thyroid cancer are at a slightly higher risk for breast cancer. More research needs to be done to better understand the basis of this association. (3/15/16)


STUDY AT A GLANCE

This study is about:

Whether there is a link between breast cancer and thyroid cancer.

Why is this study important?

Breast cancer is the most common cancer among women of all races, while thyroid cancer is the most common endocrine cancer. Previous work suggested that breast cancer and thyroid cancer occur in the same patients more often than would be expected by coincidence, causing researchers to question whether a connection exists.

Study findings: 

  1. Women with thyroid cancer were about 1.6 times more likely to develop breast cancer, compared to the general population.
  2. Women with breast cancer were about 1.2 times more likely to develop thyroid cancer, compared to the general population.

What does this mean for me?

While these results imply that an association exists between thyroid cancer and breast cancer, it is not definitive, and the extent of the increased risk is relatively small. According to the study authors, “Despite sometimes conflicting results as to the magnitude and significance of this risk, the above meta-analysis demonstrates a clear association and increase in the co-occurrence of these two malignancies. Although further studies are needed, clinicians should consider the increase in risk for second primary cancer when caring for these individuals.” Patients should continue to work with their health care provider after a cancer diagnosis for appropriate subsequent screening recommendations, and alert their health care provider when they experience changes of concern anywhere in their bodies.

Questions to ask your health care provider:

  • I have breast cancer but do not carry any genetic mutations. Am I at risk for other cancers?
  • I have thyroid cancer but do not carry any genetic mutations. Am I at risk for other cancers?
  • I have had both breast and thyroid cancer, should I consider genetic testing?
  • I am a PTEN mutation carrier. What is my risk for developing breast, thyroid, and other cancers?

 

 

IN DEPTH REVIEW OF RESEARCH

Study background:

Researchers and health care providers have observed thyroid cancer and breast cancer occurring in the same individual more often than they would have expected by chance. The two cancers are common, but as women are surviving these cancers more often due to improvements with diagnosis and treatment, researchers are focusing more on developing screenings for potential secondary cancer development for these women.

In February 2016, Sarah Nielsen and colleagues from The University of Chicago and other institutions published their work in the journal Cancer Epidemiology, Biomarkers & Prevention towards further understanding of the potential association between thyroid cancer and breast cancer. Their work is a meta-analysis, meaning they collected data from previous studies done on thyroid cancer and breast cancer association, and combined all of the information to better understand whether or not an association exists between the two cancers. 

Researchers of this study wanted to know:  

Whether the occurrence of breast cancer and thyroid cancer in the same women is happening by chance or by association between the two cancers.

Population(s) looked at in the study:

Researchers looked at data from 19 different previous research studies involving women who had thyroid cancer after breast cancer, and 18 different previous research studies involving women who had breast cancer after thyroid cancer.  

Study findings: 

  1. Women with thyroid cancer were about 1.6 times more likely to develop breast cancer, compared to the general population.
  2. Women with breast cancer were about 1.2 times more likely to develop thyroid cancer, compared to the general population.
  3. Previous studies suggest that both breast cancer and thyroid cancer use a common hormonal receptor pathway involving estrogen, which would be a potential biological link between the two cancers.
  4. Young women were more likely to have been diagnosed with both breast and ovarian cancers. This indicates that these individuals may have had a genetic mutation, which would confer additional risk of developing a second primary cancer.

Limitations:

This study is a meta-analysis, meaning the researchers combined data from multiple studies: the researchers were not involved in the design of any of the research studies used, which leads to these limitations: 1) A meta-analysis is only as strong as the combination of all of the research studies included, so a weak research study can affect the results, and 2) Each of the research studies had its own study design, so the authors of this meta-analysis could not control for differences between the studies used.

It is also important to remember that women with a mutation in the PTEN gene, which causes Cowden syndrome, are known to have an increased risk for both breast cancer and thyroid cancer. This means that their second cancer is likely to develop in the breast or thyroid.  The study authors wrote that, “It is important to remember that [Cowden syndrome] is responsible for an important, albeit small proportion of cases of breast and thyroid cancer and should be evaluated for accordingly in these individuals.” However, thyroid cancer has not been linked to other gene mutations that increase risk of breast cancer.

Conclusions:  

Ultimately, this study indicates that an association may exist between thyroid cancer and breast cancer. Women with a primary thyroid cancer or breast cancer appear to be at a slightly higher risk for subsequent breast cancer or thyroid cancer, respectively. However, more work needs to be done to better understand the biology behind this finding.  At this time, not enough information is available to change clinical recommendations for women with breast or thyroid cancer.

References

Nielsen SM, White MG, Hong S, et al. “The Breast-Thyroid Cancer Link: A Systematic Review and Meta-analysis.” Cancer Epidemiology, Biomarkers & Prevention, 25(2), February 2016. 

Posted 3/15/16

 

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