The Philadelphia Chromosome, circa 1960

The Philadelphia Chromosome, circa 1960

Less than a decade after Watson and Crick published their landmark paper on the structure of DNA, two Philadelphia researchers noticed that the blood cells of patients with chronic myelogenous leukemia (CML) had an unusually tiny chromosome. At a time when the genetic underpinnings of disease were unclear, the discovery of this abnormality—dubbed the Philadelphia Chromosome—marked the first time a specific genetic defect was linked to a cancer, paving the way for drugs that targeted the defect and turned this rare leukemia into a manageable disease.

Photo Courtesy of Alice Hungerford

1 - In 1956, Peter Nowell joined the University of Pennsylvania faculty and began what he calls “poorly defined studies of leukemia.” By rinsing blood cells with tap water before staining and mounting them on a microscope slide, Nowell inadvertently...