Can you get breast cancer from sleeping with a bra?

No: If wearing a bra is felt to induce problems because of trauma to the breast, cancer is never caused by trauma. Occasionally trauma has brought attention to the presence of a tumor. Cancer is a 3 stage event and usually induced over a period of time, initially by a virus, followed by a carcinogen or possible separate virus such as EBV which doesn't induce Ca but enhances telomerase.