New research has demonstrated how chemotherapy wakes up dormant cancer cells and helps spread the disease to healthy cells and organs—encouraging the disease to come back stronger and less treatable

News travels slowly in the world of cancer therapy. Twelve years have passed since researchers demonstrated that chemotherapy promotes cancer growth and spread by invading healthy cells that surround the cancerous area. Five years later, other researchers showed that the drugs repair a mechanism that allows cancer cells to come back stronger.

Oncologists have seen the same effects of chemotherapy every day in the clinic, but they still administer it, even to apparently healthy patients. Women with breast cancer who have been given the all-clear after surgery—which is now the preferred first-line therapy for cancer that hasn’t spread (metastasized)—are often given a course of chemotherapy.

Breast cancers that have anything greater than a 10 percent risk of recurring or spreading within five years are routinely treated with chemotherapy after surgery. It’s known as adjuvant therapy, and it’s also used if the cancer has spread to the lymph nodes.

Depending on the type of cancer, the rate of recurrence can range from 6percent to 23 percent within five years of the initial treatment. This number rises to a chilling 30 percent beyond the first five years.

Oncologists believe they can reduce this risk by up to 30 percent if they use adjuvant chemotherapy. A woman with a cancer that has a 20 percent chance of recurring in 10 years can reduce the risk to 14 percent if she has chemotherapy, they say.