Twin Breast Cancer Study

Dr. Thomas Mack of the USC California Twin Program is reaching out to twins diagnosed with breast cancer in order to understand why some women remain free from breast cancer when other women with the same genetics and upbringing are affected.

What we know:

  • As a group, twin women of any age, including identical twin women, are at the same risk of breast cancer as their friends and neighbors.
  • Even though inheritance seems to play at least some role in most cases of breast cancer, most of the healthy co-twins of women who are diagnosed with breast cancer remain free, for years, decades or permanently.
  • That suggests that some causal elements are acquired, probably long before the appearance of the disease, possibly as early as childhood.

What does the study entail?

We will ask each participant to provide a sample of saliva. From such samples we can find cells containing the unique inherited DNA code and identify any genetic breast cancer risk factors.

What questions will be asked?

  1. Generally: Participants will be asked questions relating to known predictors of breast cancer risk, most of which relate to reproductive history.
  2. Twin comparisons: Twins have compared each other since childhood, and are uniquely able to recall and agree on early differences, even after decades. Questions will be especially directed at early differences.
  3. We will ask breast cancer cases to help us obtain Pathology Reports and samples of tumor tissue from providers.

The questions should take you one-half to one hour. The more twins who participate, especially as pairs, the more likely that we can find answers to these important questions about a dreaded disease.

The study is supported by the National Cancer Institute of the National Institutes of Health. There is no cost to volunteers, except the time it takes to mark your responses and send your specimen. You will never be asked for money (your cooperation is more valuable). You may always refuse to answer any question, and you may withdraw cooperation at any time. All information will be held in complete confidence. No outside persons will have access to your identity without your permission. Results will only be released in statistical form, and no persons will ever be identified.


Click here to send an email to the study coordinator. If you would prefer to speak to someone by phone, please call 1-323-865-0828.