Familial occurrence is most evident in CLL compared with other leukemias.
— Multiple cases of CLL are found within a single family with greater frequency.
— Up to 10% of patients with CLL have a first- or second-degree relative with CLL.
— First-degree relatives of patients with lymphoplasmacytic lymphoma or Waldenström macroglobulinemia (Chap. 69) have a greater than threefold increased risk of developing CLL.