What is "melanoma lymphoma"?

I don't know. Melanoma and lymphoma are two separate tumors. Maybe you are seeing a typo or potentially a differential diagnosis and the confirmed diagnosis isn't clear. I would ask your md what it means.
No such thing. Two separate diseases. Melanoma is cancer of melanocytes (cells that produce the dark pigment, melanin, which is responsible for skin color). These cells mostly occur in skin, but are also found in other parts of the body, including the bowel and the eye. Lymphoma is a type of blood cancer develop in the lymph nodes, spleen, bone marrow, blood or other organs and eventually they form a tumor.
I don't know. It is possible that you have 2 very different cancers lumped together. Melanoma is one form of cancer and lymphoma another. They are quite different. On the other hand multiple myeloma is another type of cancer that is often confused with melanoma. I would be glad to revisit this question with you if you research the disease a little more. On the other hand, I may learn something new.