Hi, Thanks for writing in. Lymphnodes are present in most locations of the body and are a part of the immune system. These generate antibodies and increase host defenses during illness. Cancer also causes lymphnodes to enlarge and often a single lymphnode requires to be evaluated by biopsy to make sure it is not a sign of cancer. Lymphnode can also be enlarged due to infections in the region. A sacral area lymphnode might be seen due to bowel infection or any condition causing inflammation of adjacent structures. It is suggested that your father gets a cancer screening done with sacral lymphnode biopsy as recommended by his doctor. Please do not worry.