breast and thyroid cancer

I am a 61 year old female with breast and thyroid cancer.  My older sister was diagnosed with breast cancer at the age of 61.  We also have two younger sisters, and want to know if they should be genetically tested for the breast cancer genes.  None of us have been tested yet.  

Is there also a genetic link between breast and thyroid cancer?

Thank you

[Jordanna Joaquina, MS, CGC]

We recommend that you and your family (including your non-affected sisters) meet with cancer genetics for evaluation. A cancer genetic counselor can review the benefits and limitations of genetic testing for the cancer-predisposing syndromes applicable to your specific situation (if any).

Breast cancer and some types of thyroid cancer are associated with a hereditary cancer syndrome called Cowden syndrome. Almost everyone with Cowden syndrome develops hamartomas. Hamartomas are growths that are most commonly found on the skin and mucous membranes (such as the lining of the mouth and nose), but can also occur in the intestinal tract and other parts of the body. Abnormal growths on the skin and mucous membranes typically appear by a person's late twenties.