Hi, Yes, it’s called Rosai–Dorfman disease and it can have different causes, one of them is cancer. It’s still a quite mysterious disease in which we see massive amounts of so called “histiocytes” in the lymph nodes or other locations throughout the body which lead to swellings and a variety of other symptoms. Sometimes this rare disease is self-limiting, other patients need treatment like chemotherapy, radiation therapy etc. Unfortunately it can happen when someone has cancer. It is heartbreaking to learn about this situation, but please support your brother-in-law emotionally. A realistic but somewhat optimistic attitude may help to reduce pain, discomfort and activate the immune-system. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Alexander Davis, General & Family Physician