There is a paucity of studies that focus on the symptom burden of cancer patients in Singapore, particularly the clinical effects of cancer-related fatigue (CRF). Knowing that early-stage breast cancer is curable, it is of paramount importance to evaluate the clinical and biological determinants of lingering symptoms in breast cancer survivors so that appropriate psychosocial interventions can be formulated.

The investigators hypothesize that variations in clinical and biological determinants contribute to different severities of CRF among Asian breast cancer patients. Through this study, the investigators aim to evaluate the prevalence and severity of CRF among Asian breast cancer patients, and to identify the biological and clinical determinants of CRF among these patients.

This will be a multicenter, prospective, longitudinal, observational study conducted at the National Cancer Centre Singapore and KK Women's and Children's Hospital. Informed consent will be obtained from participants before the investigators proceed with data collection.

The study participants will be assessed at relevant time points. Biological determinants and symptoms associated with CRF will be assessed. The associations between changes in CRF, plasma cytokines levels, serum cortisol levels, and other clinical determinants will be elucidated.

Inclusion Criteria:

• At least 21 years of age
• Stage I-III breast cancer
• Chinese, Malay or Indian ethnics
• Surgical treatment has been performed
• Scheduled to receive four cycles of chemotherapy (doxorubicin/cyclophosphamide [AC], docetaxel/cyclophosphamide [TC], 5-fluorouracil/epirubicin/cyclophosphamide [FEC]) (total duration of 3 months) and/or radiotherapy and/or hormonal therapy
• No prior history of chemotherapy and/or radiotherapy
• Able to read and understand either English or Mandarin

Exclusion Criteria:

• Physically or mentally unable to provide verbal/written consent
• Symptomatically ill (such as infection or an allergic reaction to chemotherapy)
• Presence of another condition for which fatigue is a prominent symptom (e.g. AIDS, fibromyalgia, or rheumatoid arthritis)
• Newly started on any medications that can cause general fatigue and body weakness (e.g. a beta-blocker or antidepressant, antihistamine, or antipsychotic medication)
• Presence of neurologic or immune-related medical condition or behavior known to influence the immune system (e.g. smoking or heavy drinking)

The proposed study will be a multicenter, prospective, longitudinal, observational study conducted at the National Cancer Centre Singapore (NCCS) and KK Women's and Children's Hospital (KKH).