Chemotherapy for breast cancer is likely to cause structural brain changes, particularly in the hippocampus, which plays a key role in memory. Alterations in hippocampal subfields have not been fully described. This study aims to investigate changes in hippocampal subfield volumes in Breast cancer patients before and after chemotherapy, compared to healthy controls. Nineteen patients with breast cancer were evaluated before adjuvant therapy (T1), at one month (T2), and at one-year post-chemotherapy (T3). Healthy controls (n=23) underwent assessments at T1 and T3. Episodic memory retrieval and hippocampal subfield volumes were quantified using high-resolution proton density-weighted images segmented with HippUnfold software. Mixed-model analyses compared hippocampal volume changes at T1 between patients and healthy controls, longitudinally within the patient group (T1, T2, T3), and between the patient group and HC (T1, T3). Associations between memory retrieval scores and hippocampal subfield volumes were evaluated using general linear models. Across all assessments, patients performed worse than healthy controls. Subiculum volume was higher in patients compared to healthy controls at T1. No significant difference in memory abilities and hippocampal volume was found after chemotherapy compared to either before nor to the control group. No association between subfield volumes and episodic memory retrieval scores was observed. The effects are linked to cancer rather than chemotherapy, as no hippocampal volume changes or memory decline occurred post-treatment. Larger subiculum volume may be the result of neuroinflammation. Episodic memory deficits, independent of chemotherapy, suggest cancer-related cognitive impairment and could involved other brain regions or mechanisms.