Leukemia exemplifies the transformation of modern medicine. Once almost always fatal and poorly understood, it can now in many cases be precisely classified and treated. The path to that point was marked by errors, methodological limits, and clinical experience.

This clinical perspective was adapted by pediatric surgeon and pediatrician Jayant Radhakrishnan. A longtime practicing clinician with experience in pediatric care, he blends historical sources with daily clinical observations. His account consistently frames pathological, therapeutic, and organizational developments from the perspective of clinical medicine.

Splenomegaly and Misdiagnosis

Possible signs of leukemic disease go back far in history. Archaeological finds show changes in human remains that are consistent with modern disease patterns. A medically robust classification, however, only became possible in the 19th century when pathological anatomy and microscopy entered clinical practice. At first, visible and palpable findings dominated, especially markedly enlargement of spleen, liver, and lymph nodes.

In 1811, the Irish physician Peter Cullen described a patient whose blood appeared milky; he attributed it to acute splenitis. A few years later, the French surgeon Alfred Velpeau interpreted similar observations as pus in the bloodstream. Such interpretations matched contemporary medical thinking: Abnormal blood findings were primarily seen as signs of inflammatory or purulent processes — not as evidence of a primary disorder of the hematopoietic system.

Terminology and First Classifications

In 1845, the Scottish clinician and pathologist John Hughes Bennett made a crucial contribution to clarifying the issue. He described a young patient with pronounced hepatosplenomegaly and generalized lymphadenopathy and coined the term “leucocythemia.” More important, he posed a question that had rarely been discussed systematically: Were the blood changes a consequence of organ enlargement — or did the disease originate in the blood itself?

At the same time, Berlin pathologist Rudolf Virchow reported comparable cases. He rejected the idea of pus in the blood and interpreted the findings as a shift in the ratio of red to white blood cells. With the terms “white blood” and later “leukemia,” he created a conceptual basis for the systematic classification of hematologic diseases. His distinction between lymphatic and splenic forms paved the way for the later separation of leukemias and lymphomas.

From Blood to Bone Marrow

In the mid-19th century leukemia was diagnosed for the first time in a living patient. Where the disease originated remained unclear for a time. That question was answered independently by German pathologist Ernst Neumann and Italian physiologist and histologist Giulio Bizzozero, who identified bone marrow as the source. The focus thus shifted from peripheral organ changes to hematopoiesis itself — a decisive step in further pathogenetic understanding.

Shortly afterward, German immunologist and hematologist Paul Ehrlich introduced triacid staining, a method that for the first time allowed differentiated morphological classification of leukocytes for the first time. For the first time the cellular picture could be captured systematically. On that basis a classification of leukemias was established that lasted into the early 20th century. By about 1913, the categories acute myeloid leukemia, acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CML), and chronic lymphocytic leukemia had been introduced — a classification by cell lineage and disease course that, despite modern molecular refinement, is still used today.

Prechemotherapy Mortality

Even in the first half of the 20th century, a diagnosis of leukemia was almost synonymous with a death sentence. Retrospective analyses from the 1920s through the 1940s show median survival times of only a few months. Children with acute leukemia often died within 6 months of symptom onset.

Therapeutic attempts — from radiation and arsenic to early cytotoxic agents — produced at best temporary improvements. Medicine documented cases carefully but could do little to intervene effectively. Against this backdrop a gradual rethinking began.

Aminopterin Induced Remission

In the 1940s, Boston pathologist Sidney Farber worked daily with the corpses of children who had died of leukemia. Facing the lack of treatment options, he began, contrary to many colleagues’ advice, to try experimental approaches in severely ill patients. After it became clear that folic acid accelerated the disease course, Farber hypothesized that folate antagonists could inhibit leukemic cell growth.

In 1948, he achieved the first temporary remissions in children with ALL using aminopterin. The effects were transient but reproducible. For the first time it was shown that leukemia could be influenced pharmacologically in a targeted way.

Cooperative Clinical Trials

As therapy progressed, the need for new structures grew. At the US National Cancer Institute, oncologist and clinical pharmacologist C. Gordon Zubrod established cooperative trials and implemented randomized clinical testing. Under his leadership oncologists Emil Frei III and Emil J. Freireich developed new combination therapies and central supportive measures, including targeted platelet transfusion to prevent life-threatening bleeding.

Continuing treatment after achieving remission — instead of assuming a favorable morphologic finding meant cure — contrasted with earlier thinking. Multiagent chemotherapy thus marked a turning point in leukemia treatment — first in pediatrics and later in adult medicine.

Total Therapy Milestone

A further decisive step was taken by pediatrician and oncologist Donald Pinkel at St. Jude Children’s Research Hospital in Memphis, Tennessee. His “Total Therapy” strategy combined systemic chemotherapy, targeted central nervous system (CNS) prophylaxis to prevent CNS relapse, and long-term maintenance therapy. The approach was intensive and highly toxic, but it proved effective.

Through successive studies, long-term survival for children with ALL steadily improved. Today, long-term survival rates exceed 90%. Leukemia is therefore among the first malignant diseases for which cure became a realistic goal.

BCR-ABL Targeted Therapy

CML was also long considered incurable. A breakthrough came in 1960 when US pathologist Peter Nowell and cytogeneticist David Hungerford described a characteristic chromosomal defect that later became known as the Philadelphia chromosome. Chicago human geneticist Janet Rowley clarified the genetic basis by identifying a reciprocal translocation between chromosomes 9 and 22 as the cause.

The recognition that the resulting BCR-ABL fusion protein acted as a constitutively active tyrosine kinase, identified a clear molecular target for therapy. The introduction of the TKI imatinib in 2001 (the first successful BCR-ABL TKI) fundamentally changed the prognosis of CML and, in many cases, turned a formerly fatal disease into a long-term, controllable chronic condition.

This story was translated from Univadis Germany, part of the Medscape Professional Network.