Breast cancer is one of the most common cancer types worldwide and accounts for approximately 31% of all cancers in women. The global incidence of breast cancer is increasing, making it a significant public health problem. Advances in breast cancer management, including surgery, chemotherapy, radiotherapy, and hormone therapy, have contributed to reduced mortality rates. However, despite these positive developments, chemotherapy-related cognitive impairment, commonly referred to as "chemobrain," may occur.

Chemotherapy-induced cognitive impairment may manifest as deficits in memory, learning, attention, motor functions, executive functions, visual-spatial abilities, and information processing speed. These impairments negatively affect patients' quality of life and daily functioning.

In this study, cognitive education activities were designed and implemented to address these impairments. These activities aimed to support attention, memory, and executive functions and to minimize cognitive deficits. The purpose of this study was to examine the effects of cognitive activities applied to breast cancer patients receiving chemotherapy on cognitive functions, depression levels, and odor recognition abilities.

The study sought to answer the following research questions:

1. What is the effect of cognitive education activities on odor recognition ability in breast cancer patients receiving chemotherapy?
2. What is the effect of cognitive education activities on cognitive functions in breast cancer patients receiving chemotherapy?
3. What is the effect of cognitive education activities on depression levels in these patients?

This randomized controlled trial was conducted between March 2025 and February 2026 at the oncology outpatient clinic and chemotherapy unit of Gulhane Training and Research Hospital. The study aimed to evaluate the effects of cognitive education activities on cognitive function, depression levels, and odor recognition ability in breast cancer patients receiving chemotherapy. A total of 120 patients who met the inclusion criteria were enrolled in the study. Eligible participants were between 18 and 65 years of age, literate, diagnosed with breast cancer, had received at least one cycle of chemotherapy, were continuing treatment, and had no diagnosed neurological or cognitive disorder before or during chemotherapy. In addition, participants had a Standardized Mini-Mental Test (SMMT) score of 24 or below. Participants were randomly assigned to intervention (n=60) and control (n=60) groups using a computer-generated randomization method. During the study, 12 participants withdrew for various reasons, and the study was completed with 108 participants (54 in each group). The study was designed as a single-blind, pre-test/post-test randomized controlled trial. The intervention group received structured cognitive education through printed booklets, face-to-face sessions, and weekly telephone counseling. The cognitive activity program was designed to stimulate attention, memory, executive functions, and language skills. Four cognitive activity booklets with progressively increasing difficulty levels were developed. Since chemotherapy sessions were scheduled every three weeks according to the hospital protocol, each booklet was structured to be completed over a three-week period. Face-to-face sessions were conducted every three weeks, resulting in a total of five sessions over a 12-week period. During these sessions, participants completed structured cognitive activities included in the activity booklets, such as sudoku, puzzles, sentence completion, pattern recognition, word derivation, coloring, and reading comprehension exercises, all of which were designed to support cognitive functions. Weekly telephone follow-ups were conducted to enhance adherence to the intervention. To assess olfactory function, odor identification tasks were performed using non-transparent containers. Familiar scents such as lavender, coffee, lemon, orange, onion, rose water, and cinnamon were used. The control group received routine care without any cognitive intervention during the study period. After completion of the study, the control group was also provided with cognitive activity training and the educational materials used in the intervention. Data were collected using a sociodemographic data form, an odor identification test, the Standardized Mini-Mental Test (SMMT), the Functional Assessment of Cancer Therapy - Cognitive Function (FACT-Cog) scale (Version 3), and the Beck Depression Inventory (BDI). Measurements were conducted at baseline and at 12 weeks following the initial assessment.

Inclusion Criteria:

Participants were eligible if they met all of the following criteria:

• Aged between 18 and 65 years
• Literate
• Diagnosed with breast cancer
• Had received at least one cycle of chemotherapy and were currently undergoing chemotherapy
• Had a Standardized Mini-Mental Test (SMMT) score of 24 or below
• Had no diagnosed cognitive, neurological, or psychiatric disorder prior to chemotherapy

Exclusion Criteria:

Participants were excluded if they met any of the following criteria:

• Age over 65 years
• SMMT score above 24
• Presence of brain metastases
• Presence of neurological or medical conditions affecting cognitive function
• Diagnosed psychiatric disorder
• Current use of central nervous system depressants, stimulants, or psychiatric medications
• History of alcohol or substance abuse

Withdrawal Criteria:

Participants were withdrawn from the study if any of the following occurred:

• Discontinuation of chemotherapy treatment
• Inability to attend follow-up visits regularly
• Failure to complete the cognitive activity booklet tasks
• Loss of contact or inability to reach the participant
• Voluntary withdrawal from the study
• Death during the study period

Individual participant data will not be shared publicly. The data were collected as part of a single-center randomized controlled trial conducted for academic thesis purposes and will not be made available for external use.

The randomization sequence was generated by an independent statistician using a computer-based randomization tool. Outcome assessors and data analysts were blinded to group allocation. Data were coded as Group A and Group B during analysis to ensure blinding, and group identities were revealed only after the completion of statistical analyses.