Family clustering of blood cancers as a risk factor for lymphoid neoplasms.

Family aggregation of cancer was significantly more common among 588 incident cases with lymphoid neoplasms than among 631 controls (OR: 1.4; 95%CI= 1.1-1.8, p value=0.004). This association was of particular relevance among cases of multiple myeloma and chronic lymphocytic leukemia, with a 2-fold increased risk, the latter also showing an almost 4-fold increased risk of family aggregation of hematologic cancers.