The word “cancer” comes from the Greek word karkinos, which means “crab.” By the late fifth century BCE, Greek physicians were using this term to describe deadly tumors whose swollen veins spread outward from a central mass, resembling the legs of a crab. The Romans later translated karkinos into the Latin word cancer, which also means crab, and that Latin form is the one that stuck in English and most Western languages.
Why a Crab?
Ancient physicians offered several explanations for comparing tumors to crabs, and the reasons shifted depending on who you asked. The most common explanation was visual: the network of distended veins radiating from a tumor looked like a crab’s outstretched legs. As one ancient text put it, “as the crab has legs spreading around its body, in the same way are the veins in this illness; they are spread by the abnormal tumor in a shape of crab.”
But not everyone focused on appearance. Some physicians emphasized the crab’s behavior instead. A crab seizes whatever it grabs and refuses to let go, and cancer behaves the same way in the body. Stephanus, a physician lecturing in Alexandria in the seventh century AD, neatly summarized both schools of thought: “it is called karkinos either because of the aggressivity of the animal, or because the veins located in the affected part resemble tentacles, as the legs of a crab do.” Paul of Aegina, writing around the same period, added that the disease “adheres to any part which it seizes upon in an obstinate manner like the crab.”
Before the Greeks Had a Name
The disease existed long before anyone called it cancer. Two ancient Egyptian documents, the Edwin Smith and George Ebers papyri, contain descriptions of tumors written around 1600 BCE, and their source material is believed to date as far back as 2500 BCE. The Smith papyrus describes surgical approaches, while the Ebers papyrus covers pharmacological and even magical treatments. Based on these records and hieroglyphic inscriptions, Egyptian physicians could already distinguish harmful tumors from harmless ones. They simply didn’t have a single unifying word for what we now call cancer.
From Karkinos to Karkinoma to Cancer
The Greeks actually used two related terms. Karkinos referred to the crab and, by extension, to the tumor itself. Karkinoma (literally “crablike mass”) described the broader condition, and it’s the direct ancestor of the modern medical term carcinoma. Hippocrates is widely credited with establishing this naming convention, linking the word to the visual resemblance between a tumor’s central body with its spreading extensions and the shape of a crab.
The Roman physician Celsus, working in the first century AD, translated karkinos into Latin as cancer. Around a century later, the influential Greek physician Galen introduced a separate term: oncos, the Greek word for “swelling,” which he used to describe tumors more generally. That word oncos is the root of “oncology,” the modern medical specialty devoted to treating cancer. So two of the most important words in cancer medicine trace back to two different Greek physicians choosing two different metaphors: one saw a crab, the other simply described a lump.
Cancer and Canker Split Apart
When the word arrived in English, it didn’t come as a single clean term. It spawned several variants: cancer, canker, kanker, and chancre all share the same root in karkinos. For a time, “canker” was essentially an anglicized pronunciation of the Latin “cancer,” with the hard “k” sound preserved. The two words coexisted in medical writing for centuries.
Over time, though, the meanings drifted apart. “Cancer” narrowed to mean the malignant disease specifically. “Canker” became a catchall for a wider range of conditions: bodily ulcers, mouth sores, venereal lesions, and various other non-cancerous problems. This split has occasionally confused historians who encounter “canker” in old medical texts and aren’t sure whether the author meant what we’d now call cancer or something far less serious. Today the two words feel completely unrelated, but they started as the same word spoken with different accents.
A 2,500-Year-Old Metaphor
What’s remarkable is how durable this naming choice turned out to be. A visual comparison made by Greek physicians watching veins splay around a tumor became the permanent identity of one of humanity’s most feared diseases. The crab metaphor traveled from Greek to Latin to Old French to Middle English, surviving every linguistic transition intact. Even the zodiac constellation Cancer (the Crab) shares the same Latin root, which is why the astrological symbol occasionally causes a moment of unease on medical forms. The word has outlasted every theory about what causes the disease, every treatment era from ancient surgery to modern immunotherapy. Twenty-five centuries later, we still call it the crab.