Previous studies have largely been conducted in geriatric patients in order to evaluate medication complexity in hospitals, where chronic diseases and polypharmacy are frequently observed [10, 26, 27]. Therefore, this is the first study that investigated medication regimen complexity in hospitalized cancer patients. The medications used for comorbidities and supportive therapies, in addition to anticancer treatment, led to the consideration of cancer patients as high-risk individuals in terms of adverse patient outcomes such as unplanned hospitalization, decreased quality of life, and increased prevalence of DRPs, including non-adherence.

In studies evaluating medication regimen complexity, it is seen that the MRCI score varies between 9 and 45 [22, 27,28,29,30]. Although the MRCI score in this study was lower than the studies in the literature, it may be explained by the fact that the patients in the study were younger and the number of chronic diseases per patient was lower compared to other studies. Cancer is a remarkably complex disease, and intensive anticancer treatment, long outpatient infusions, and additional visits for supportive care further complicate the management of cancer. Taken together, the need for prolonged and increasingly complex treatment can be viewed as unique stressors in cancer [31]. A high MRCI score does not always indicate “very complex” treatment. Therefore, when assessing the complexity, the clinical condition of the patient, the differences in administration route of the drugs, and the duration of drug usage (such as chronic treatment) should also be taken into consideration.

Similar to the results of hospitalized patients, an increase in patients’ MRCI scores was observed with hospitalization in this study [22, 26]. An increase in the number of medications and changes in drug formulations (e.g., switching oral to transdermal opioids) as a result of patients having new diagnoses (e.g., initiation of oral suspension for the management of mucositis) or modification of treatment (e.g., prescribing low molecular weight heparin for the risk of venous thromboembolism) during hospitalization can increase the medication regimen complexity [4]. The increase in MRCI score seen under the control of physicians and clinical pharmacists during hospitalization is not an uncontrolled increase, but is due to medication regimen optimization.

Unplanned hospitalization was one of the most common health care outcomes studied in association with the MRCI score. Because the MRCI score significantly changes during the course of the hospital stay, the discharge MRCI score can reasonably be used to predict the risk of a post-discharge readmission. In the study, the MRCI score assessed at the discharge was associated with unplanned hospitalization within 30 days, which supports that the MRCI score may predict a marker of hospitalizations and can be used to identify patients at risk [8, 30]. It was previously demonstrated that opioids, anticoagulants, non-steroidal anti-inflammatory drugs, cardiovascular system drugs, sedatives, anxiolytics, and antipsychotics had been associated with recurrent unplanned hospitalizations [9]. Similarly, the intensive use of these groups of drugs, especially analgesics and cardiovascular system drugs, in the treatment of cancer patients participating in the study may be a reason for unplanned hospitalization within a 30-day period after discharge.

The studies investigated the association between medication complexity and the duration of hospitalization, encouraging the use of the MRCI tool in daily clinical practice [32, 33]. Given the fact that the health condition of cancer patients is generally critical, the use of the MRCI assessment tool in practice will be valuable to predict patients at risk [9].

Improving patient adherence is crucial to reducing hospital readmissions. Physician-pharmacist collaboration on the modification of drug treatment and the provision of information for patients about drugs may reduce the perceived medication regimen complexity and increase patient adherence. In an oncology ward, patient education on drug treatment provided by a clinical pharmacist has positive effects on medication adherence [20, 34,35,36]. In this study, the clinical pharmacist was involved in the multidisciplinary healthcare team for the provision of education. The MARS score at follow-up outpatient visit was found to be higher than the score at the time of hospitalization. It is thought that the increase in adherence, despite the increase in the MRCI score, is due to the effect of the medication education given to the patients. The fact that cancer patients have frequent outpatient clinic visits compared to other chronic patients, and that these outpatient clinic visits involve various specialties, may result in high disease awareness. This is thought to be a factor that increases patients’ adherence. Over time, patients may establish a routine in the use of medication or lose the habitual use of medication. Therefore, the measurement of MARS at different times may result in an increase or decrease in adherence, depending on individual characteristics.

Although there have been studies [14, 15, 37] which evaluated the medication treatment burden perceived by patients with chronic diseases, none of these studies included cancer patients. Drug-related factors such as the requirement of the patients to use different dosage forms (patches, suspensions) or additional instructions to use (changing fentanyl patches every 48 h) can make the treatment more complex and ultimately result in an increase in the patient’s perceived burden for cancer treatment.

An increase in the perception of drug-related burden decreases patients’ adherence to drug treatment [37]. The observed increase in adherence in patients who responded “usually and always” to the statement of “I can easily adapt to the times when I have to take my medication” in the MCQPP questionnaire, which may indicate adherence, may reflect the positive effect of patient education provided by the multidisciplinary team. Understanding the perception related to treatment burden, as well as medication regimen complexity in patients, and designing therapeutic care plans appropriate for patients’ lifestyles may create opportunities for healthcare professionals to provide individualized patient care [14]. Development and routine use of validated tools for evaluation of medication complexity and patients’ perceived burden on treatment will help to improve the quality of service provided in patient care processes. Such services can be designed to include the MRCI scale, serving as a patient prioritization tool that predicts outcomes such as unplanned hospitalization, increased length of hospital stay, and drug interactions, in particular for patients who are at high risk and have a burden on health costs.

The medication burden may also arise from DRPs. Although there were not many DRPs observed for anticancer drugs in this study, drugs used in the treatment of infection and supportive care resulted in a more frequent occurrence of DRPs. Since the clinical pharmacist made recommendations to address DRPs and physicians accepted 83.3% of these recommendations, the majority of the DRPs were resolved. This may have indirectly reduced the impact of treatment burden.

The study has limitations; subgroup analyses could not be performed for cancer type and treatment protocols due to limited numbers of patients included. The study was conducted in a single center; however, it is one of the major/well-known cancer care centers in the country, which may reflect the tertiary care practices for oncology. Since this study was conducted in the medical oncology wards and did not include patients in a palliative care ward, the patient empowerment in early palliative care is still needed to be explored in future studies. As no previous study evaluated the medication-related complexity in cancer patients, the study results cannot be compared and interpreted any further. In addition, patients’ adherence to drug therapy was evaluated in a very short period of time after discharge, which may not reflect the real-world situation. While many validated quality of life scales generally evaluate the effect of the disease on the patients’ daily living, since there is no validated scale that evaluates the impact of perceived burden of medication complexity, researchers assessed this situation by developing the MCQPP. Due to time constraints, the MCQPP could not be validated during the study process. The intention is to conduct the requisite studies for the validation of the MCQPP in order to create a standardized scale that will facilitate evaluation from the patient perspective. It may lead to the development of such instruments that comprehensively evaluate the burden related to disease, medication, and treatment processes in cancer patients.

Future studies should be designed to investigate the burden of medication complexity in the long term, and to surrogate the impact of clinical pharmacy services in the management of treatment complexity by inclusion of a control group in patients with cancer.