ABSTRACT Breast cancer is one of the most common types of cancer worldwide and often requires chemotherapy as part of its treatment. However, chemotherapy can affect the nutritional status of patients due to side effects such as nausea, vomiting, and loss of appetite. This study aims to analyze the relationship between chemotherapy cycles and nutritional status in breast cancer patients undergoing chemotherapy at Sentra Medika Cibinong Hospital. This research employed a quantitative method with a cross-sectional approach, using univariate and bivariate data analysis with the chi-square test. The sampling technique used was purposive sampling, involving 40 respondents out of 64 breast cancer patients who underwent chemotherapy in January 2025. Nutritional status was assessed using the Malnutrition Screening Tool (MST) questionnaire. The results showed that 55% of respondents were in their third chemotherapy cycle (with drug administration lasting 6–8 hours), 50% had a normal body mass index (BMI), and 52.5% had good nutritional status. A significant relationship was found between chemotherapy cycles and nutritional status, with a p-value of 0.010 (p < 0.05). Future researchers are advised to include other variables such as daily food intake, physical activity, stress levels, and social support, which may also influence nutritional status. Keywords: Breast Cancer, Chemotherapy Cycle, Nutritional Status, Malnutrition Screening Tool (MST). ABSTRAK Kanker payudara merupakan salah satu jenis kanker dengan angka kejadian tinggi di dunia dan sering memerlukan kemoterapi sebagai bagian dari pengobatannya. Namun, kemoterapi dapat memengaruhi status nutrisi pasien akibat efek samping seperti mual, muntah, dan penurunan nafsu makan. Penelitian ini bertujuan untuk menganalisis hubungan antara siklus kemoterapi dan status nutrisi pada pasien kanker payudara yang menjalani kemoterapi di Rumah Sakit Sentra Medika Cibinong. Penelitian menggunakan metode kuantitatif dengan pendekatan cross-sectional dan analisis data univariat serta bivariat menggunakan uji chi-square. Teknik pengambilan sampel yang digunakan adalah purposive sampling dengan jumlah responden sebanyak 40 orang dari 64 pasien yang menjalani kemoterapi pada Januari 2025. Status nutrisi diukur menggunakan kuesioner Malnutrition Screening Tool (MST). Hasil penelitian menunjukkan bahwa 55% responden menjalani siklus kemoterapi ke-3 (dengan pemberian obat selama 6–8 jam), 50% memiliki indeks massa tubuh kategori normal, dan 52,5% menunjukkan status nutrisi yang baik. Terdapat hubungan yang signifikan antara siklus kemoterapi dan status nutrisi dengan nilai p = 0,010 (p < 0,05). Peneliti selanjutnya disarankan untuk menambahkan variabel lain seperti asupan makanan harian, aktivitas fisik, tingkat stres, dan dukungan sosial yang dapat memengaruhi status nutrisi. Kata Kunci: Kanker Payudara, Siklus Kemoterapi, Status Nutrisi, Malnutrition Screening Tool (MST).