Cancer, lymphoma, non-Hodgkins: A lymphoma is a cancer that develops in the lymphatic system. The most common symptom of non-Hodgkins lymphomas is a painless swelling in the lymph nodes in the neck, underarm, or groin. Non-Hodgkins lymphomas are diagnosed with a biopsy of an enlarged lymph node. Follow-up examinations are important after lymphoma treatment. Most relapses occur in the first 2 years after therapy.