What are the symptoms of hereditary breast cancer?

Same as regular: Breast cancer. Only about 3% of the breast cancers are due to inherited defects and these cancers have the same symptoms as regular/sporadic cancer, i.e., mass/lump in the breast.

Young/Bilateral: Breast cancer symptoms are no different whether one has the hereditary or environmental form of the disease. However, women with the hereditary form tend to be diagnosed at an earlier age and have a higher incidence of cancer developing in both breasts. The telltale sign, of course, is a pattern of breast +/- ovarian cancer in multiple relatives.