| Summary: | Abstract Acute lymphoblastic leukemia (ALL) is the most common childhood leukemia, while the other types, acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), and chronic myeloid leukemia (CML) are much rarer. While data on familial risks for childhood ALL have been emerging, such data for the other childhood leukemias are hardly available. We aim to fill in the gap of knowledge by assessing familial clustering of each childhood leukemia with childhood and adult leukemia and with any cancer. We identified 4461 childhood leukemias from the Swedish Cancer Registry and obtained their family members from the Multigeneration Register. Standardized incidence ratios (SIRs) were 3.34 for singleton siblings both diagnosed with ALL before age 20 years and 1.64 for those who had a family member diagnosed with ALL in adult age. Other childhood leukemias showed no familial risk, but childhood ALL risk was increased to 1.40 when adult family members were diagnosed with CLL. Childhood ALL was associated with endometrial cancer, and female ALL patients showed increased risk when family members were diagnosed with testicular cancer, melanoma, and skin squamous cell carcinoma. Childhood CLL was associated with rectal cancer, and childhood AML was associated with pancreatic and bladder cancers. As most of these associations are reported for the first time, there is a need to replicate the findings from independent sources.
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