Patients with cancer are considered "immunocompromised." This means that, because of the cancer and the cancer treatment, the immune system does not function normally, which decreases its ability to fight off infection and disease. This immunocompromised condition places these patients (who probably had been in contact with the TB bacteria, resulting in latent, or inactive, TB) at risk for active TB. Latent TB does not cause symptoms or signs of active TB infection. It is very important to identify patients who are at risk for developing active TB, so that they can receive timely treatment for TB.