The immune system protects the body from harmful bacteria and other organisms. Cancer and cancer treatment may weaken the immune system in a number of ways:

• Some types of cancer—especially lymphomas and leukemias—may stop the bone marrow from producing enough healthy white blood cells, which work to fight off infection.
• Chemotherapy and radiotherapy may reduce the number of white blood cells produced by your bone marrow.
• Surgery creates a break in the skin, making it more prone to infection.

If your immune system has been affected, there are certain precautions that can help avoid infection. These include:

• Avoiding people with infections
• Avoiding places where there is a risk of infection
• Avoiding crowds
• Talking to your doctor before you have any vaccines
• Maintaining good personal hygiene
• Keep a clean mouth
• Protecting your central line or central catheter (if you have one) from bacteria and damage
• Avoiding foods that may contain harmful bacteria