Leukemia is overwhelmingly a disease of aging. The median age at diagnosis is 68, and nearly 60% of all new cases occur in people 65 and older. This isn’t coincidental. The biological machinery that keeps blood cell production in check gradually breaks down over decades, and a lifetime of accumulated genetic damage, environmental exposures, and changes in the bone marrow all converge to make leukemia far more likely in later life.
Genetic Damage Builds Up Over a Lifetime
Every cell in your body accumulates genetic errors as you age. These mutations arise from ordinary processes: copying errors when cells divide, chemical reactions from normal metabolism, and the slow breakdown of DNA repair systems. In young people, each cell carries fewer than 1,000 of these small genetic changes. By the time someone is over 70, that number climbs to roughly 5,000 per cell.
Beyond these small-scale errors, larger structural problems in chromosomes also become more common. About 1% of cells in young people carry a significant chromosomal abnormality like a translocation, deletion, or duplication. In older adults, that figure rises to around 5%. Most of these mutations never cause cancer on their own. But over decades, the sheer volume of accumulated damage increases the odds that a critical combination of mutations will land in a blood stem cell, giving it a growth advantage that eventually spirals into leukemia.
Clonal Hematopoiesis: A Pre-Leukemia State
Before leukemia develops, many older adults pass through a precursor stage called clonal hematopoiesis of indeterminate potential, or CHIP. In CHIP, a blood stem cell acquires a mutation that gives it a slight competitive edge over its neighbors. That mutant cell begins producing a disproportionate share of blood cells, creating a “clone” that can be detected on blood tests. You feel perfectly healthy, have no cancer symptoms, and follow-up testing finds no malignancy.
CHIP becomes increasingly common with age. It’s relatively rare before 50 but present in a significant portion of people over 70. The condition doesn’t mean you’ll develop leukemia, but it does raise the risk. Think of it as a step along a path: the clone already has one or two dangerous mutations, and if additional hits accumulate in the right genes, the clone can transform into a full blood cancer. CHIP also correlates with higher rates of heart disease and overall mortality, suggesting that these rogue clones affect the body in ways beyond cancer risk.
Which Types of Leukemia Affect Older Adults
Not all leukemias are the same, and the types that predominate in older adults differ from those seen in children and younger people. Chronic lymphocytic leukemia (CLL) is the most common leukemia in developed countries, with a median age at diagnosis above 70. It tends to progress slowly, though survival improvements over the past decade have benefited younger patients more than older ones.
Acute myeloid leukemia (AML) is the other major type in this age group. AML is aggressive and often arises from a related condition called myelodysplastic syndrome (MDS), in which the bone marrow produces abnormal, poorly functioning blood cells. Among patients 66 and older with MDS, about 12% eventually transform to AML. That rate jumps considerably in higher-risk MDS subtypes, reaching nearly 32% in cases with excess immature cells (called blasts) in the bone marrow. This MDS-to-AML pathway is one of the most common routes to leukemia in the elderly population.
Previous Cancer Treatment
Older adults who survived an earlier cancer are at elevated risk for what doctors call therapy-related leukemia. Certain chemotherapy drugs and radiation therapy, while effective against the original cancer, can damage the DNA of healthy blood stem cells in ways that surface years later. Therapy-related cases account for roughly 10% to 20% of all AML and MDS diagnoses, and that share is growing as more people survive their first cancer and live long enough for these secondary effects to emerge.
The timing depends on the type of treatment. Chemotherapy drugs that work by directly damaging DNA (alkylating agents) typically cause leukemia after a latency period of 5 to 10 years, often preceded by a phase of MDS before progressing to full AML. A different class of drugs (topoisomerase II inhibitors) can trigger leukemia on a shorter timeline, sometimes within just a few years, and usually without the MDS stage in between.
Smoking and Tobacco Exposure
Cigarette smoking is one of the most firmly established modifiable risk factors for myeloid leukemias. A large meta-analysis found that current smokers have a 45% higher risk of developing myeloid blood cancers compared to people who never smoked. Even former smokers carry a 23% elevated risk.
The risk increases with heavier and longer use. People who smoked a pack a day or more had a 32% higher risk than nonsmokers, and those with 20 or more years of smoking history had a 30% increase. When broken down by specific disease, smoking raised the risk of AML by 43% and MDS by 48%. For someone in their 60s or 70s who smoked for decades, this cumulative exposure contributes meaningfully to their overall leukemia risk on top of the age-related changes already happening in their bone marrow.
Chemical and Environmental Exposures
Benzene is the single most well-documented environmental cause of leukemia. The U.S. Department of Health and Human Services classifies it as a known human carcinogen, and long-term exposure to high levels causes leukemia directly. Benzene is found in gasoline, industrial solvents, cigarette smoke, and certain manufacturing processes. Older adults who spent careers in petroleum refining, rubber manufacturing, shoe production, or chemical plants may carry decades of accumulated benzene exposure that raises their risk well above the general population.
Other environmental factors linked to leukemia include formaldehyde, certain pesticides, and high-dose ionizing radiation. For most people, these exposures are low enough to pose minimal individual risk. But combined with the natural accumulation of genetic mutations over a lifetime, even moderate occupational exposures can tip the balance.
Why Age Itself Is the Biggest Factor
The core reason leukemia clusters in older adults is that aging is, at its foundation, the accumulation of cellular damage. DNA repair becomes less efficient. The immune system grows less effective at recognizing and eliminating abnormal cells. The bone marrow environment changes in ways that may favor mutant clones over healthy ones. None of these processes cause leukemia on their own, but together they create a landscape where a blood stem cell that has picked up the right combination of mutations can expand unchecked.
The numbers tell the story clearly. People aged 65 to 74 account for 26% of new leukemia cases. Those 75 to 84 account for another 22%. And adults over 84 make up nearly 10%. Combined, the over-65 population represents close to 60% of all new leukemia diagnoses despite being a fraction of the total population. For most older adults diagnosed with leukemia, the cause isn’t a single event or exposure but the convergence of decades of small, compounding insults to the blood-forming system.