Cancer is a deadly disease and effective treatment is very important. Because of the long duration of treatment and the toxicity of treatments, we are dealing with the problem of adherence and treatment compliance. Low adherence to oral chemotherapeutic agents has been associated with poor treatment outcomes, increased toxicity, and higher healthcare costs. Studies have shown that cancer patients are 16% less likely to adhere to oral chemotherapy than patients receiving infusion therapy under physician supervision . Given the importance of the direct impact of adherence on treatment efficacy and treatment resistance, we wanted to investigate adherence to oral anticancer drugs among cancer patients in our clinic.
The average adherence to oral therapy in our study was high with high motivation and knowledge. Patient-related factors that may influence adherence include cognitive impairment, comorbidities, gender, psychopathology, and other medications taken. We excluded patients with cognitive impairment from the study. When gender was examined, no correlation was found between patient motivation and knowledge level and gender in this study. In the literature, some studies have shown that treatment adherence was better in women than in men, an inconsistent pattern [18, 19] and two studies [20, 21] showed that female gender was associated with unfavourable outcomes in treatment adherence and self-care in diabetes and cardiac rehabilitation. In our study, the motivation and knowledge level of the young population was significantly higher than that of the geriatric population (≥ 65 years), and statistically significant. In a study by Barron et al of 2816 patients who continued tamoxifen treatment, patients aged 35–44 years and older than 75 years were more likely to discontinue tamoxifen compared with a reference group of women aged 45–54 years .
As expected, we found that the motivation and knowledge level of patients with higher educational level were significantly higher (p < 0.0001 for both). However, in some studies, there was no association between adherence and education level [23, 24]. In addition, social support may be important for adherence. However, in our study, there was no association between living status with family and marital status with motivation and knowledge level . However, in our study, more than 90% of patients lived with their family and were married.
ECOG- PS status is a very important parameter in the cancer treatment process, especially in selecting optimal therapies and determining prognosis. It has been shown that patients with poor performance status (PS) have an increased risk of chemotherapy toxicity and poor treatment outcomes compared to patients with better performance status . In this study, it was found that motivation and knowledge levels were statistically significantly lower in patients with a high ECOG-PS score.
Another issue is the relationship between duration of treatment and adherence. Adherence to long-term therapy for chronic diseases averages 50% in industrialised countries . When the duration of patients' medication use was examined in our study, it was found that both motivation and knowledge levels were high among patients who had been taking oral anticancer medications for more than 12 months. This was in contrast to what was reported in the literature regarding the duration of tamoxifen use. In the study by Barron et al, the cumulative discontinuation rate of tamoxifen within 1 year of starting treatment was 22.1%. After a follow-up period of 3.5 years, the cumulative discontinuation rate increased to 35.2%. Age and history of antidepressant use were among the predictors of observed persistence . However, in a study examining treatment adherence and duration of medication use in schizophrenia patients, patients who had been on medication for 1–5 years were compared with those who had been on medication for less than 1 year, and adherence was found to be lower in those who had been on medication for a short time . In a study of 7525 patients measuring treatment adherence with antidepressants, the discontinuation rate in the first 4 months was 54% . These data are similar to our findings, which may indicate that the critical period for treatment adherence is the early phase of therapy. The daily or cyclical nature of treatment was also examined in the study, as it may influence treatment adherence. It was found that motivation and knowledge levels were significantly higher in those who took oral anticancer medications cyclically than in those who took their medications daily. Adherence to cyclical treatments may have increased as patients perceived the importance of individualised follow-up of their own treatments.
In addition to the MMAS-6 questions, patients were also asked about reasons for treatment discontinuation. Most treatments were discontinued after the scheduled program or due to lack of efficacy, only 6.9% of patients discontinued treatment due to side effects, and only one patient discontinued treatment at his own request. It is very important that patients are informed in detail about the efficacy of the treatment and possible toxicities when adhering to the treatment. In this study, all but one patient discontinued treatment on the advice of physicians.
Subgroup analysis according to patients' diagnoses and medications could not be performed because of the heterogeneity of the groups. However, patients with breast cancer, who accounted for more than half of our patients, were highly motivated and had a high level of knowledge. The most commonly used drugs in this study were letrozole, capecitabine, and tamoxifen. Patients taking capecitabine had very high levels of motivation and knowledge. However, these data could not be statistically analyzed because of the heterogeneity of the groups. This was one of the limitations of our study.
There is no "gold standard" method for assessing adherence and compliance. The MMAS-6 has been used in many studies, including those with cancer patients. After some inadequacies were identified in this scale, 2 additional questions were added and the Morisky Medication Adherence Scale-8 (MMAS-8) was developed. However, we used this scale because MMAS-6 has Turkish validation. This was another limitation of our study. In addition, our study was conducted during the pandemic period and when the number of patients reached 300, the study was terminated. Since it was a pandemic, only the patients who could come to the hospital could be included in the study.