This is a history article, not medical information. It does not describe what any person should do about their own health.
No single “first”
There was no one technology that was the first for cancer diagnosis. X-rays showed masses almost immediately after 1895, and each later imaging method gave a new way to notice a tumor. A scan on its own also does not confirm cancer; throughout this history, a tissue sample examined with clinical microscopes has remained the usual way to establish a diagnosis, and imaging mainly helps find, locate and follow abnormalities.
Radiographs in the early years
Within a few years of the Roentgen discovery, doctors were using X-rays to look at bones, the chest and the digestive tract. Bone tumors and some lung masses appeared as unusual shadows. Chest radiography became a mainstay in the first half of the twentieth century, largely because of tuberculosis, and the same films sometimes revealed lung tumors. The X-ray was also tried as a treatment for cancer very early, which blurred the line between imaging and therapy for a time.
Mammography
The breast is soft tissue with little natural contrast, so early mammography took decades to mature. In 1913 the German surgeon Albert Salomon examined X-rays of removed breast tissue and compared them with the findings, showing that tumors and small calcium deposits could be seen. In the 1930s Stafford Warren in the United States reported using X-rays on breasts in living patients. Raul Leborgne in Uruguay emphasized careful technique and the significance of calcifications in the 1950s. Charles Gros in France and Robert Egan in Texas helped standardize methods around 1960, and dedicated machines with better tubes and compression developed in the following years. Large studies in the following decades examined whether regular screening lowered deaths from breast cancer. The findings, and the balance of benefits and harms such as false alarms, are still discussed, so this article does not offer conclusions.
Contrast studies and early body imaging
Barium and iodine-based contrast agents helped outline tumors in the stomach, bowel and urinary tract in the early to mid-twentieth century. Some earlier agents were later withdrawn because of long-term harm, a reminder that safety knowledge was still developing.
Nuclear medicine
In the 1950s and 1960s, radioactive tracers allowed clinicians to see where certain tissues took up substances. Scans of the thyroid, bones and liver became routine in some centers, and the gamma camera gave a way to survey the whole body for areas of unusual activity. These images were fuzzy but offered something X-rays could not: a view of function.
CT, MRI and ultrasound
When computed tomography appeared in the early 1970s, its first clinical use was on the brain. Body scanners soon followed, and tumors in the abdomen, chest and elsewhere could be seen in cross-section without surgery. Before this, finding such masses sometimes required exploratory operations. MRI added strong contrast in soft tissue, and ultrasound provided a radiation-free way to look at organs such as the liver or the ovaries.
PET and combined scanners
Positron emission tomography, using a glucose-like tracer called fluorodeoxyglucose (FDG), became the best-known tool for showing metabolic activity in tumors. FDG was developed in the 1970s, and combined PET/CT scanners around the year 2000 placed the metabolic picture on top of the anatomical one. As with all the methods above, results need interpretation, since inflammation and normal tissue can also take up tracer.
Why it is “forgotten”
The story is often compressed into a single device, but the real history involved many small steps by physicians, physicists and technicians. Pioneers of mammography such as Salomon, Leborgne and Egan are far less familiar than the CT and MRI Nobel laureates. Their work shows how cancer imaging came less from one invention than from decades of refinement.