Leukemia is a cancer of the blood-forming tissues characterized by the rapid growth of abnormal blood cells in the bone marrow. These cancerous cells, typically immature white blood cells, crowd out healthy cells and impair the body’s ability to produce normal blood components. While often associated with childhood, leukemia affects individuals from infancy through advanced age. Age is the most important factor determining the specific type of leukemia diagnosed and significantly influences the treatment approach.
The Bimodal Nature of Risk
Leukemia affects all age groups, but the incidence rate follows a unique pattern known as a bimodal distribution. This means the disease has two distinct peaks in diagnosis rates across the human lifespan. The first, smaller peak occurs in early childhood, where leukemia is the most common cancer diagnosed in children and teens.
The second, much larger peak begins to rise significantly around age 55 to 60, with the highest rates occurring in adults aged 65 to 74 and beyond. This pattern highlights that the vast majority of all leukemia cases—over 90%—are diagnosed in adults. This dual-age pattern is linked to the different types of leukemia that arise at different stages of life.
Pediatric Leukemia Prevalence
Leukemia is the most common cancer in children and teens, peaking between ages two and five years. Acute lymphoblastic leukemia (ALL) is the predominant form, representing approximately three out of four childhood cases. This acute form is characterized by the rapid production of abnormal, immature white blood cells called lymphoblasts.
Acute myeloid leukemia (AML) is the next most common type in children, accounting for most of the remaining cases. Chronic forms of the disease, such as Chronic Myeloid Leukemia (CML) and Chronic Lymphocytic Leukemia (CLL), are extremely rare and are predominantly disorders of older adulthood.
Understanding Adult Onset Leukemia
The risk of developing leukemia increases steadily with age, with the median age of diagnosis for most types falling in the mid-to-late sixties. Chronic lymphocytic leukemia (CLL) is the most common type diagnosed in adults, typically affecting individuals around age 70. CLL is a slower-growing cancer of the B-lymphocytes, where symptoms may not be noticeable for years.
Acute myeloid leukemia (AML) is the most common acute leukemia in adults, with the average age of diagnosis being approximately 68 years. AML is a fast-progressing disease that requires immediate treatment, and its risk increases significantly after age 45. Chronic myeloid leukemia (CML) is also more common in older adults, with an average diagnosis age of 64. CML is distinct because it is strongly linked to the Philadelphia chromosome, a specific genetic abnormality.
How Age Impacts Treatment and Outcomes
Age at diagnosis is a major factor influencing both the choice of treatment and the long-term outlook for a patient. For children with ALL, the five-year survival rate is now around 90%, reflecting remarkable improvements in pediatric oncology. This favorable outcome is often due to the ability of younger bodies to tolerate intensive chemotherapy regimens.
In contrast, older adults often have a less favorable prognosis, especially with acute leukemias like AML, where the five-year survival rate falls dramatically for those over age 65. Older patients frequently have other health conditions, known as comorbidities, which limit their tolerance for aggressive chemotherapy. Furthermore, the leukemia often presents with more adverse genetic characteristics in older adults, contributing to the difficulty in achieving long-term remission.