Lymphoma cancer. Light micrograph of a section through a secondary lymphoma, a cancer of lymphoid tissue, from lymph nodes in the armpit. This cancer has spread from a primary tumour in the breast. The spread of cancer from one site to another is known as metastasis. The lymphatic system forms a major part of the immune system, and cancer severely weakens the immune response. This makes the patient more susceptible to infections, and makes normally harmless infections life threatening. Once a cancer has spread beyond its point of origin, the chances of a cure are low. Magnification unknown.