Chris McQueen finished treatment for leukemia a year and a half ago, but the ads for fake cures never stopped.

Juice cleanses to cure cancer, “natural” cancer treatments, clinics in Mexico promising full recovery with little chemotherapy — all appeared on McQueen’s mobile phone during routine oncologist visits and monthly blood work.

McQueen and others have taken to social media to vent about companies known as data brokers tracking their whereabouts via their smartphones’ location data, connecting it with other data gathered about them and then drawing inferences about their health to sell to companies hawking unproven treatments.

“It makes me feel sick to my stomach,” said McQueen, who lives in San Diego.

More than 92 percent of patients in a 2022 American Medical Association survey said they believed their health data should not be available for purchase.…