If you’re asking how someone gets leukemia, the honest answer is: in most cases, we don’t know the exact trigger. Leukemia develops when the DNA in a single blood-forming cell mutates, causing it to multiply uncontrollably and crowd out healthy blood cells. These mutations can be inherited, acquired through environmental exposures, or — most commonly — arise from random copying errors during normal cell division. There’s rarely a single “cause” you can point to.
That said, decades of research have identified clear risk factors that increase the odds. Some you can control; others you can’t. This guide breaks down the science behind how leukemia develops, who’s most at risk, and what patients and caregivers should actually watch for — written by a hematology content team that reviews these cases daily.
What Exactly Happens Inside the Body?
Leukemia starts in the bone marrow, the spongy tissue inside your bones where blood cells are made. Normally, your marrow produces white blood cells, red blood cells, and platelets in a tightly regulated process. In leukemia, a genetic mutation disrupts this process in a precursor cell — a cell that hasn’t fully matured yet.
That mutated cell begins dividing rapidly, producing millions of abnormal white blood cells (sometimes called blasts) that don’t fight infection properly. These dysfunctional cells pile up in the marrow and spill into the bloodstream, leaving less room for healthy cells. The result: anemia, bleeding problems, and a crippled immune system.
The specific mutations matter. Some activate oncogenes (genes that accelerate cell growth), while others knock out tumor suppressor genes (the brakes on cell division). For example, the Philadelphia chromosome — a translocation between chromosomes 9 and 22 — drives about 95% of chronic myeloid leukemia (CML) cases.
The 7 Major Risk Factors for Leukemia
Research from the American Cancer Society, NCI, and large epidemiologic studies has identified these key risk factors. I’ve organized them by whether they’re modifiable or not:
| Risk Factor | Type | Key Details |
|---|---|---|
| Age | Non-modifiable | Median diagnosis age is 67. Risk rises sharply after 55 — but ALL peaks in children ages 2–5. |
| Smoking | Modifiable | Linked to ~20% of AML cases. Benzene in cigarette smoke damages bone marrow stem cells. |
| Chemical exposure | Modifiable | Prolonged benzene exposure (petroleum, rubber industries) significantly raises AML risk. |
| Prior chemotherapy or radiation | Partially modifiable | Alkylating agents and topoisomerase II inhibitors can cause therapy-related AML 2–10 years later. |
| Genetic syndromes | Non-modifiable | Down syndrome carries a 10–20x higher risk of childhood leukemia. Li-Fraumeni, Fanconi anemia, and ataxia-telangiectasia also increase risk. |
| Family history | Non-modifiable | Having a first-degree relative with CLL roughly doubles your risk. Most leukemias, however, are NOT inherited. |
| High-dose radiation exposure | Non-modifiable (historical) | Atomic bomb survivors showed leukemia rates 5–10x above baseline. Diagnostic X-rays pose negligible risk. |
A critical point for caregivers: most people with one or even several risk factors never develop leukemia. And many leukemia patients have no identifiable risk factors at all. The disease is not caused by anything the patient “did wrong.”
Early Symptoms That Shouldn’t Be Ignored
Leukemia symptoms mimic dozens of benign conditions, which is why it’s frequently caught late — or found incidentally on routine blood work. Here’s what to watch for:
- Persistent fatigue that doesn’t improve with rest (from anemia — hemoglobin often below 10 g/dL at diagnosis)
- Frequent or severe infections — more than 3–4 per year, or infections that don’t resolve with antibiotics
- Easy bruising or bleeding — especially petechiae (tiny red dots on skin), bleeding gums, or heavy nosebleeds. Platelet counts below 50,000/µL increase bleeding risk.
- Unexplained weight loss — losing more than 10% of body weight over 6 months without trying
- Night sweats that drench your sheets
- Bone or joint pain, particularly in children — caused by marrow expansion
- Swollen lymph nodes, spleen, or liver — painless lumps in the neck, armpits, or groin
Acute leukemias (AML, ALL) tend to hit fast — symptoms escalate over days to weeks. Chronic leukemias (CML, CLL) can simmer for years before anyone notices. Many CLL patients are diagnosed only because a routine CBC shows an elevated white blood cell count above 20,000/µL.
How Leukemia Is Diagnosed
The diagnostic workup typically follows this sequence:
- Complete blood count (CBC) with differential — the single most important screening test. Abnormal blast cells in the peripheral blood are a red flag.
- Peripheral blood smear — a pathologist examines blood cells under a microscope to identify abnormal morphology.
- Bone marrow biopsy — the gold standard. A diagnosis of acute leukemia requires ≥20% blasts in the marrow (per WHO criteria).
- Flow cytometry — identifies cell surface markers to classify the leukemia subtype precisely.
- Cytogenetics and molecular testing — detects specific chromosomal abnormalities (like Philadelphia chromosome) and gene mutations (FLT3, NPM1, TP53) that guide prognosis and treatment decisions.
Getting the subtype right matters enormously. The difference between, say, APL (acute promyelocytic leukemia) and other AML subtypes can mean the difference between a 90% cure rate and a much harder road.
Treatment at a Glance
Treatment depends entirely on leukemia type, patient age, genetic mutations found, and overall health. Here’s a simplified overview:
- Chemotherapy — still the backbone for acute leukemias. Induction therapy aims for complete remission, followed by consolidation.
- Targeted therapy — drugs like imatinib (Gleevec) transformed CML from a fatal disease into a manageable chronic condition. Five-year survival for CML now exceeds 70%.
- Stem cell transplant — potentially curative for high-risk or relapsed cases, but carries significant risks including graft-versus-host disease.
- CAR-T cell therapy — approved for relapsed/refractory ALL in patients up to age 25 and certain lymphomas. Response rates above 80% in some trials.
- Watch and wait — standard for early-stage CLL. Many patients live 10–15+ years without needing treatment.
When to See a Doctor
Don’t wait if you notice any combination of the symptoms listed above, especially if they persist for more than two weeks. Specifically, seek urgent evaluation if you experience:
- Unexplained bruising appearing without trauma
- A fever above 100.4°F (38°C) that won’t break, combined with fatigue
- Rapidly growing lumps in the neck, armpits, or groin
- Extreme pallor, dizziness, or shortness of breath at rest
Ask your doctor for a CBC with differential. It’s inexpensive, widely available, and can detect most leukemias. If results are abnormal, push for a referral to a hematologist — not a wait-and-recheck approach.
Frequently Asked Questions
Can you “catch” leukemia from someone else?
No. Leukemia is not contagious. You cannot get it through physical contact, sharing food, breathing the same air, or any other form of exposure to someone who has it. It arises from internal genetic mutations in your own blood cells.
Does leukemia run in families?
Rarely. Most leukemias are sporadic — meaning they occur without any family history. CLL has the strongest familial link among leukemias, with first-degree relatives having roughly a 2–4x increased risk. Inherited cancer syndromes (Li-Fraumeni, Fanconi anemia) also raise risk, but these are uncommon.
Can stress or diet cause leukemia?
There is no convincing scientific evidence that psychological stress or any specific diet causes leukemia. Chronic stress may affect immune function broadly, but a direct causal link to leukemia has not been established in clinical studies. Focus on known modifiable risk factors: avoid smoking and minimize benzene exposure.
Why do some children get leukemia?
Childhood ALL — the most common pediatric cancer — often involves genetic mutations that occur before birth, during fetal development. Some researchers believe a “two-hit” model applies: an initial prenormal genetic change, followed by an abnormal immune response (possibly triggered by infections) in early childhood. The good news: cure rates for childhood ALL now exceed 90% with modern protocols.
If I have a risk factor, should I get screened?
There’s no routine screening test for leukemia like there is for breast or colon cancer. However, if you have a known genetic syndrome, prior chemotherapy/radiation exposure, or a strong family history of blood cancers, discuss periodic blood work with your doctor. An annual CBC is reasonable for higher-risk individuals.
