Thinness is not a criterion for determining whether breast cancer is advanced or not. Thinness may also be caused by excessive psychological pressure and medication. 1. Advanced stage of breast cancer: in advanced stage of breast cancer, the lumps are usually large, and the lymph nodes in the axilla are fused, and the patients may also have local or distant metastasis. Patients will have localized or distant metastasis. They will have symptoms such as local skin ulceration, infection and bleeding. Due to metastasis, body organs are dysfunctional and unable to absorb nutrients, thus leading to body wasting; advanced breast cancer cannot be determined by a single symptom, but requires systematic examination. 2. Excessive psychological pressure: as breast cancer is a more serious malignant tumor disease, it may bring more psychological pressure to the patients, resulting in low food intake or digestive system problems, which may lead to emaciation. 3. Due to medication: the skinny body may also be caused by the chemotherapy drugs taken by the patient, which will bring serious adverse reactions to the body during the chemotherapy period, leading to vomiting, nausea, diarrhea and so on, resulting in the patient eating too little or not being able to fully absorb the nutrients, which leads to the skinny body. Breast cancer patients should have a correct mindset and take active treatment in order to have the disease under effective control.