Dr. Sheldon Greenfield, whose pioneering research found that older patients with breast and pancreatic cancer got subpar treatment and that patients who grill their doctors during consultations receive better care, died Feb. 26 at his home in Newport Beach. He was 86.

The cause was colon cancer, his daughter Lauren Greenfield said.

Greenfield was a founder and director of the Center for Health Policy Research at UC Irvine, and a leader of the Medical Outcomes Study, involving more than 22,000 patients and 500 physicians, which determined in 1986 that doctors often ordered exorbitant and unnecessary tests and referred patients to a specialist when a primary care doctor or a nurse practitioner could have delivered equally good care.

Harvard University President Alan Garber praised Greenfield as “a towering figure in health care research.”

“His influence extended more widely than even he could have known, through the Medical Outcomes Study and so much else,” Garber said in an email.

In 1991, Greenfield and collaborators including his wife, Dr. Sherrie Kaplan, found that too many conversations about care were dominated by doctors. They recommended a protocol that included a 20-minute coaching session for patients before they consulted their physicians.

“When doctors dominate the medical interview, patients don’t do as well as when the patient exerts more control,” Greenfield told The New York Times that year.

Diabetes patients who asked questions about dosage and volunteered other symptoms during checkups, according to a study in 1995, recorded a 15% drop in blood sugar after two months. Similar results were found in studies of patients with ulcers and hypertension.

As that study’s principal author, Greenfield explained that the researchers focused on adult diabetes because it is prevalent and because the proper treatment can prevent complications that make it one of the most expensive chronic diseases to treat.

Four years earlier, a research team that Greenfield led had concluded that while 96% of women ages 50 to 69 with breast cancer received the appropriate minimal level of acceptable care, only 83% of otherwise healthy women 70 and older did. (The study defined “appropriate” as either removal of the entire breast and some surrounding tissue or removal of the lump and the nearest lymph node, followed by radiation treatment.)

“The lives of these patients may be needlessly shortened,” Greenfield said.

In 1989, a group led by Greenfield found that older men who developed cancer of the prostate were less likely than younger men to receive the best available treatment.

He also expressed concern about the lack of appropriate follow-up care for cancer patients. He attributed this in part to the fact that, in many cases, insurance companies, health plans and Medicare don’t cover the necessary tests and examinations.

“Successful cancer care doesn’t end when patients walk out the door after completion of their initial treatments,” Greenfield told the Times.

The work he and Kaplan did “addressed the effects of the doctor-patient relationship on the outcomes of chronic illness,” Dr. Harold Sox, an emeritus professor at the Geisel School of Medicine at Dartmouth College, said in an email. “They showed that better doctor-patient partnerships paid off in better patient outcomes.

“We hear a lot about the shortage of primary-care physicians,” Sox added. “Dr. Greenfield’s work showed that good primary care matters a lot.”