Pathologists and doctors are using a 19th century definition of cancer to diagnose the disease, which leads to unnecessary treatment in some cases, according to Otis Brawley, Chief Medical Officer of the American Cancer Society. 

Speaking on Thursday at the 2012 TEDMED conference, Brawley called for a 21st century approach to cancer diagnosis; and a modern, genomics-based appreciation of cancer so that patients don’t undergo surgeries and chemotherapy for tumors that pose little threat. 

Pathologists still use drawings made in 1840 to determine whether the cells in a biopsy are cancerous or not, said Brawley. When a lump is deemed to be cancerous, surgery often follows. But as many as 25% of breast cancers and, by some estimates, 60% of prostate cancers could be left untreated and merely monitored, he said.

Brawley said the medical community needs to use genomic sequencing to identify the genetic signals of those cancers that doctors need to watch and those that need to be treated. This could be achieved by sequencing tumors from different cancer patients and looking for a genetic “profile” that is associated with dangerous, stable, or benign cancers.