1. From Breastcancer.org "Underwire bras do not cause breast cancer. Only one scientific study has looked at the link between wearing a bra and breast cancer. There was no real difference in risk between women who wore a bra and women who didn't wear a bra."
Fact: There is no such study, and no reference is given to support the claim.
2. From the American Cancer Society "There are no scientifically valid studies that show wearing bras of any type causes breast cancer."
Fact: There are numerous studies. See references.
3. From TriStar Skyline Medical Center " The American Cancer Society conducted a study of more than 1,500 women that found no association of bra use and breast cancer risk."
Fact: There is no such study. And again, no reference was given to support the claim.
4. From the Fred Hutchinson Cancer Research Center “Our study found no evidence that wearing a bra increases a woman’s risk for breast cancer,” said Lu Chen, a researcher in the Public Health Sciences Division at Fred Hutch. “The risk was similar no matter how many hours per day women wore a bra, whether they wore a bra with underwire, or at what age they began wearing a bra.”
Fact: This study did not include any bra-free women. That means there was no control group. You cannot come to a conclusion of the impacts of bra usage without a bra-free control. This flaw was mentioned by the study's authors in their study text, but not in the press release above.
5. From the American Cancer Society "Because of the attention this book generated, ACS scientists Ted Gansler, M.D. and Ahemdin Jemal, Ph.D. conducted a small study in 2009 published in the Breast Cancer Journal (subscription required) to explore the biological mechanism behind the carcinogenic bra hypothesis. They looked at survivors of shoulder or upper extremity melanoma. Many patients with this cancer have their underarm lymph nodes removed surgically, which substantially impedes lymphatic drainage from the breast. If lymphatic obstruction caused breast cancer, one would expect those who got the surgery to have higher rates of breast cancer. Their analysis found no increase in breast cancer among those who had surgery to remove the lymph nodes. The authors caution that their study was preliminary, but concluded the “results do not support the hypothesis of lymphatic disruption being a breast cancer risk factor.”"
Fact: This "study" was actually a letter to the editor in the ACS's Breast Journal, so it was not a peer reviewed study. The text does reveal that they did find that there was a significant increase in skin cancer in women who had had lymph node dissection, which supports the model that impaired lymphatic drainage leads to cancer. In addition, their sampling was too small to come up with a significant conclusion about the breast cancer link. And they looked for breast cancer within 5 years or so of the lymph node surgery. This is not a good model for breast cancer caused by chronic constriction from bras, which may take decades to develop into cancer.