To investigate concordance in survival time among first-degree relatives with lymphoid malignancies.
By linkage of national Swedish registers, we identified 66,430 patients diagnosed with a lymphoid malignancy 1958-2016 with information on first-degree relationships and follow-up until 2017. Among these, we identified pairs of first-degree relatives with any (N=3,326) or a similar (N=690) lymphoid malignancy subtype. We defined survival in the first-degree relative as good, expected or poor based on tertiles of deviance residuals from a multivariable Cox regression model. Next, we used Cox regression to estimate hazard ratios (HR) of death with 95% confidence intervals (CI) among patients, using the survival of their first-degree relative as exposure and adjusting for confounders.
There was no concordance in survival among first-degree relatives with any lymphoid malignancy (HR =1.00 (reference), HR =1.02, 95% CI 0.89-1.17, HR =1.12, 95% CI 0.98-1.27, P =0.08). Among first-degree relatives with indolent lymphoma, including chronic lymphocytic leukemia, those with a first-degree relative with an expected or poor survival had worse outcome compared to those with a first-degree relative with good survival (HR =1.44, 95% CI 0.82-2.53, HR =1.79, 95% CI 1.07-3.00, P =0.03).
Our results support a role of inherited factors in the outcome of indolent lymphoma, including chronic lymphocytic leukemia.

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