Nearly one-third of women with breast cancer went against their doctor’s advice and chose not to begin or complete the recommended adjuvant anti-cancer therapy to kill residual tumor cells following surgery, according to a study led by a Johns Hopkins Bloomberg School of Public Health researcher.

A survey that included 2,754 breast cancer patients in Florida and Pennsylvania during a two-year period found that this “treatment discordance”—not following a doctor’s recommended treatment plan in its entirety—was more likely among patients who reported a general distrust of medical institutions and insurers. The patients’ trust or distrust of their own doctors did not seem to be a factor.

Small studies in the past have found that some patients refuse their doctors’ advice and choose not to undergo or complete adjuvant therapy after breast cancer surgery.

The new study, published in the journal Cancer Epidemiology, Biomarkers & Prevention, is by far the largest evaluation of this issue, and suggests that the avoidance of adjuvant therapy is significant and is linked to a general distrust in the healthcare system.

“If we want more women with breast cancer to complete their treatment, we’ll need to deal with their beliefs about the healthcare system—and I do think we can modify those beliefs,” said Lorraine T. Dean, ScD, assistant professor in the Bloomberg School’s Department of Epidemiology and the study’s lead author.

Adjuvant therapy for breast cancer normally consists of a course of chemotherapy, hormone therapy or radiation treatment, and is meant to kill any cancer cells not removed by the initial surgery. Research has shown that adjuvant therapy on average reduces the likelihood of breast cancer’s recurrence and increases patients’ chances of long-term survival.

Yet it has long been clear that many patients either do not start their prescribed adjuvant therapy or start it but do not complete it. Cancer epidemiologists would like to know the causes of this treatment discordance, or noncompliance, in the hopes of improving treatment compliance, and thus improving patients’ long-term outcomes.

Prior studies, which were smaller in sample size and geographic scope, have linked breast cancer adjuvant treatment discordance to patients’ lack of trust in the general healthcare system, but have not been clear about whether or not distrust in the system is separate from distrust in physicians. Dean and colleagues sought to clarify this issue of trust with a large survey of breast cancer patients in two major U.S. states. The researchers mailed survey questions to all women in Pennsylvania and Florida cancer registries who were diagnosed with invasive but still localized breast cancer between 2005 and 2007 and were under the age of 65 at the time of diagnosis.

The response rate was 61 percent and the final sample included 2,754 women. Sixty-nine percent of patients were white, 27% were Black/African-American and four percent identified as another race or ethnicity. About 69.8% of these women indicated that they had received all of the adjuvant treatments their doctor had recommended. The remainder, 30.2%, indicated that they had elected not to receive at least one prescribed adjuvant treatment. More than half of the latter, or 18 percent of the cohort, had not undergone some or all of the recommended hormone therapy; the rest were evenly split between discordance with radiation treatment and discordance with chemotherapy.

“While it is surprising in general that nearly one-third of patients are not following up with recommended adjuvant treatment, some earlier, more localized studies have reported even higher discordance rates, and it’s possible that our own figures would have been higher if we had followed patients for more than two years,” Dean noted.

The survey asked participants about their trust in their doctors and in the healthcare system in g