Leukemia is not a single disease, and the people most likely to develop it depend on which type. Overall, the highest rates occur in adults over 65, in males, and in people with certain genetic conditions or chemical exposures. But one major form, acute lymphoblastic leukemia (ALL), peaks in early childhood, making leukemia unusually broad in who it affects.
Age Is the Strongest Single Factor
Most leukemia diagnoses happen in older adults. Chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML), the two most common forms in adults, are rarely seen before age 45 and climb steeply after 65. The median age at diagnosis for both is in the late 60s to early 70s. Chronic myeloid leukemia (CML) follows a similar pattern, with most cases appearing in middle age and beyond.
The exception is ALL, the most common cancer in children. It represents about 20% of all cancers diagnosed in people under 20, accounting for more than 3,000 new cases each year in the United States alone. Rates are highest in children aged 1 to 4 years, at roughly 75 cases per million. After early childhood, ALL incidence drops sharply before rising modestly again in older adults. So while leukemia overall skews older, the childhood peak of ALL is a defining feature of who gets this disease.
Males Have Higher Rates Across Every Major Type
Biological sex plays a consistent role. Globally, about 269,500 males are diagnosed with leukemia each year compared to roughly 205,000 females. That gap holds across all four major subtypes. Projected 2025 cases in the United States illustrate the pattern clearly:
- CLL: 14,340 males vs. 9,350 females
- AML: 12,060 males vs. 9,950 females
- CML: 5,610 males vs. 3,950 females
- ALL: 3,450 males vs. 2,650 females
In childhood, leukemia is about 1.7 times more common in boys than in girls, a trend seen worldwide. Males also tend to have poorer survival rates once diagnosed. The one exception is infant leukemia (birth to age 2), where female infants actually have a slightly higher incidence. Researchers believe hormonal differences and sex-linked genetic factors both contribute, though the exact mechanisms are still being worked out.
Down Syndrome and Other Genetic Conditions
Certain inherited conditions dramatically raise leukemia risk, especially in children. Down syndrome (trisomy 21) is the most well-known example. Children with Down syndrome face an estimated 10- to 20-fold increase in leukemia risk compared to other children, with some studies reporting figures as high as 100-fold depending on the subtype measured.
A unique condition called transient abnormal myelopoiesis, or TAM, occurs almost exclusively in newborns with Down syndrome. It’s a pre-leukemic blood disorder that often resolves on its own within the first 90 days of life, but in some cases it progresses to a form of myeloid leukemia specific to Down syndrome. Children with Down syndrome also develop ALL at higher rates, and their genetic background appears to amplify the effect of certain inherited susceptibility genes that exist in the general population.
Other genetic syndromes linked to elevated leukemia risk include Fanconi anemia, Li-Fraumeni syndrome, and neurofibromatosis, though these are far rarer than Down syndrome.
Family History Raises Risk Modestly
Having a close relative with leukemia does increase your chances, though the effect is smaller than many people assume. A Swedish population study found that children with a first-degree relative (parent or sibling) who had ALL faced about 3.2 times the average risk of developing ALL themselves. That sounds dramatic in relative terms, but because childhood ALL is uncommon to begin with, the absolute risk remains low.
The family connection extends across leukemia types. Children whose adult family members had CLL showed a 1.4-fold increased risk of developing ALL. For AML, having a family member with any leukemia raised the risk by about a third, though that increase was not statistically conclusive. The takeaway: family history matters, but it’s one piece of a larger puzzle rather than a strong predictor on its own.
Benzene and Workplace Chemical Exposure
Among environmental risk factors, benzene exposure has the strongest evidence. Workers in oil and gas extraction, petroleum refining, and shoe manufacturing face the highest occupational exposures. A large Swiss study found that AML risk increased in a dose-dependent manner: the more benzene exposure a worker accumulated, the higher their risk. Workers in the highest exposure category had roughly 35% greater AML mortality risk compared to unexposed workers.
Benzene isn’t just an occupational hazard. It’s also present in cigarette smoke, gasoline fumes, and certain industrial solvents. For most people, daily exposure is well below the levels linked to leukemia in workplace studies, but long-term, low-level exposure may still matter, particularly for smokers.
Previous Cancer Treatment
One of the more sobering risk factors is prior treatment for a different cancer. Therapy-related AML develops as a direct consequence of chemotherapy, radiation therapy, or both. In a study of 306 patients with therapy-related myeloid leukemia, 40% had received chemotherapy alone, 14% had received radiation alone, and 46% had undergone a combination of the two.
Two categories of chemotherapy drugs carry the most risk. Alkylating agents (a class of older, broadly acting cancer drugs) tend to cause leukemia that develops slowly over 5 to 7 years after treatment, often passing through a stage where the bone marrow produces abnormal cells before full leukemia emerges. A different class, topoisomerase II inhibitors, can trigger leukemia more quickly, sometimes within 1 to 3 years. The risk is a trade-off: these treatments save lives when used against the original cancer, but they leave a small percentage of survivors vulnerable to a secondary blood cancer years down the road.
Putting It All Together
No single factor determines who gets leukemia. The highest-risk groups are older adults (especially men), children between ages 1 and 4 for ALL specifically, people with Down syndrome or other genetic syndromes, workers with sustained benzene exposure, and cancer survivors who received certain chemotherapy or radiation treatments. Most people who develop leukemia have no obvious risk factor at all, which is part of what makes the disease unpredictable. But understanding who faces elevated risk helps explain why screening, early symptom recognition, and workplace protections matter for different populations at different life stages.