Final answer:
Lymph nodes can become secondary cancer sites through a process called metastasis, where cancer spreads from the primary tumor to other parts of the body via the lymphatic system or blood, resulting in new cancers called metastases. Lymphoma is a type of cancer that originates within the lymph nodes themselves.
Step-by-step explanation:
Lymph nodes can become secondary cancer sites through a process known as metastasis. When cancer spreads, it typically moves from the primary tumor through three main routes. One is the local invasion of contiguous tissues; another is via the lymphatic system to nearby or regional lymph nodes; and the third is through the blood to distant sites, leading to new cancers called metastases. Interestingly, cancer can also originate within the lymph nodes themselves, which is the case with lymphoma. The swelling of lymph nodes can be a symptom of lymphoma, which is a cancer of the lymphocytes (a type of white blood cell).