The incidence of lymphoma in first-degree relatives of patients with Hodgkin disease and non-Hodgkin lymphoma: results and limitations of a registry-linked study.

BACKGROUND: The precise incidence of familial Hodgkin disease (HD) and non-Hodgkin lymphoma (NHL) in first-degree relatives is unknown. Through record linkage using two population-based sources, the authors estimated the risk of HD and NHL in family members of lymphoma probands.
METHODS: The authors identified 8,037 first-degree relatives of 2,606 lymphoma cases (28.5% HD, 71.5% NHL) treated between 1970 and 1993 in 3 hospitals in Israel via the family file of the Population Registry. The authors linked this file with the Israel Cancer Registry, then calculated the standardized incidence ratio (SIR) by dividing the observed number of cases with the expected, adjusting for age, gender, calendar year, and continent of origin.
RESULTS: The family file yielded incomplete ascertainment of relatives (for 771 probands, no relatives were identified). Twenty cases of lymphoma--6 HD and 14 NHL--were identified among relatives of lymphoma patients. The SIR for HD was 1.15 (95% confidence interval [CI]: 0.42-2.51) and for NHL 1.71 (95% CI: 0.93-2.87), considering the entire population of first-degree relatives. SIRs among siblings of lymphoma probands were 3.12 (95% CI: 1.01-7.29) for HD, 2.16 (95% CI: 0.45-6.31) for NHL, and 2.68 (95% CI: 1.15-5.27) for all lymphomas. There were 4 HD/HD, 1 NHL/NHL, and 3 NHL/HD sibling pairs. For HD/HD and NHL/NHL sibling pairs, the interval between lymphoma occurrence in proband and sibling was 1-4 years, whereas for HD/NHL pairs this ranged from 16 to 21 years.
CONCLUSIONS: The risk of lymphoma among siblings of lymphoma probands was over 2.5-fold that of the general population and lower among other family members. The temporal proximity of HD/HD and NHL/NHL sibling pairs argues for environmental as well as genetic etiology. This method was hampered by incomplete data.