Define lymphoma.

A lymphoma is a malignancy of the immune system that is characterized by an abnormal proliferation of lymphocytes and related cell types. Most lymphomas begin in lymph nodes and are divided into Hodgkin’s and non–Hodgkin’s lymphomas. The non–Hodgkin’s lymphomas are further subdivided into T-cell and B-cell subtypes.

Willemze R: New concepts in the classification of cutaneous lymphomas, Arch Dermatol 131:1077–1080, 1995.