High grade non-Hodgkin's lymphoma. Light micrograph of a section through lymphoid tissue with high grade non-Hodgkin's lymphoma (cancer). A lymphoma is a cancer of the cells in the lymphatic system, which is the major part of the immune system, and permeates the entire body. The cancerous cells here are seen as having large irregular nuclei (dark purple). The chaotic replication of cells within the lymph nodes leads to a swelling of the node, which is often the only early symptom. The high grade form is fatal in most cases, although radiotherapy and anti-cancer drugs may prolong life. Magnification unknown.