Hormone receptor-positive breast cancer is the most common type of breast cancer worldwide, and ASCO guidelines suggest that women diagnosed with hormone receptor-positive breast cancer should receive adjuvant endocrine therapy with tamoxifen for 5 years. The trade-off between the potential risk of side effects and the potential benefit of taking adjuvant endocrine therapy for up to 5 years is important. A study of women with breast cancer who received adjuvant endocrine therapy such as tamoxifen found that their expectations of side effects influenced the incidence and severity of side effects. The study, published in Annals of Oncology, a leading international cancer journal, found that women who had higher expectations of side effects before receiving adjuvant endocrine therapy experienced more and more severe side effects. They experienced nearly twice as many side effects as patients who had benign expectations or thought the side effects would be less severe. The researchers believe this finding is important because women who are too fearful of side effects or who have a poor quality of life may not be suitable for adjuvant endocrine therapy; in fact, these may also affect the outcome and prognosis of treatment. However, if expectations can be used to predict the risk of side effects, then interventions (psychological counseling) may be able to reduce the risk of side effects and thus improve outcomes. Yvonne Nestoriuc (Department of Psychosomatic Medicine and Psychotherapy, University Medical Center Hamburg, Germany), who led the study, said: “Our results suggest that expectancy as a clinically relevant predictor affects the long-term outcome of hormone therapy. Reducing treatment expectations can reduce the burden of long-term side effects and optimize subsequent antitumor therapy in survivors. The study was a clinical trial conducted in 111 female breast cancer patients enrolled in the Breast Cancer Center at the University of Marburg in Germany. Enrollment was based on being surgically treated, hormone receptor positive, and scheduled to start adjuvant endocrine therapy such as tamoxifen or exemestane (aromatase inhibitors). At the start of this clinical trial, investigators asked them about their expectations of side effects from adjuvant endocrine therapy and evaluated 107 subjects after 3 months and 88 subjects after 2 years, respectively. At the start of this clinical trial, 9 (8%) patients said they did not expect side effects from endocrine adjuvant therapy, 70 (63%) subjects said they expected moderate side effects, and 32 expected moderate to severe side effects. At the end of 2 years, medication adherence was related to side effects at 3 months and expectations at the beginning of treatment. Women who had low expectations of side effects prior to treatment had an 87% adherence rate, while those who had high expectations of side effects prior to treatment had a 69% adherence rate. Women who had higher expectations of side effects at the beginning of the study implied a 1.8-fold increase in the probability of side effects and lower quality of life over the two years of treatment than those with low or moderate expectations. The investigators took into account factors such as socio-demographic and medical factors (including symptoms experienced prior to the start of the study and menopausal symptoms) that could affect the results of the experiment and made appropriate adjustments based on these factors. After adjustment, the expected values for treatment remained independent, clinically relevant risk factors. Side effects included arthralgia in 71% of patients, weight gain in 53%, and hot flashes in 47%. The women also reported symptoms that were not directly attributable to treatment, including back pain in 31% of patients, dyspnea in 28%, and dizziness in 26%. Those with low expectations of adjuvant endocrine therapy before treatment appeared to declare that they would not tolerate adjuvant endocrine therapy in the long term, especially after three months of treatment when the first serious side effects were confirmed. One of the limitations of this study is that approximately 40% of patients eligible for enrollment did not participate in such a clinical trial. The decision of those who did not want to participate in the clinical trial may have influenced the results because these patients who did not want to participate in the clinical trial themselves had poor expectations of endocrine therapy. Professor Nestoriuc and his colleagues are conducting a randomized controlled study to test whether raising women’s expectations of endocrine adjuvant therapy is really effective. This involves having a psychologist or trained medical staff counsel patients before and during the first few months of treatment, emphasizing the benefits they will receive from adjuvant endocrine therapy, explaining what side effects to expect, and telling patients what to do about them.