What type of cancer begins in immune system cells specifically in lymphocytes?

Lymphoma is the correct answer because it specifically originates from lymphocytes, which are a type of white blood cell integral to the immune system. Lymphoma represents a category of cancers that typically develop in lymphatic tissue, including lymph nodes, spleen, and bone marrow, where lymphocytes are produced and reside.

In contrast, leukemia involves the proliferation of abnormal blood cells originating primarily in the bone marrow, affecting the blood and bone marrow rather than lymphatic tissue specifically. Myeloma, while also a cancer of blood cells, originates from plasma cells, which are differentiated B lymphocytes, and tends to affect the bone marrow more directly. Carcinoma refers to malignancies arising from epithelial cells and is unrelated to the immune system's lymphocytes. Therefore, lymphoma is the most accurate choice as it directly relates to the cancer that begins in lymphatic immune cells.