Whether a breast 4mmx5mm nodule is serious or not should depend on the nature of the nodule, which is generally categorized into benign nodules that are not serious and malignant nodules that are more serious. 1. benign nodules: breast 4mmx5m benign nodules are usually caused by tumor-like changes in the breast tissue, most of them are not serious, because the nodule volume is small, so the patient if you actively carry out the relevant treatments, and maintain a good state of mind, in general, will not cause too much impact on the body. 2. Malignant nodules: breast 4mmx5m malignant nodules may be more serious, and may cause malignant changes in the condition, such as lung metastasis, bone metastasis, etc. It is recommended that patients should go to the hospital in time to undergo surgical treatment and cooperate with the doctor to carry out post-care. Patients with breast nodules are advised to go to regular hospitals in time and receive standardized treatment under the guidance of doctors. In the process of treatment, patients should pay attention to the mood, try to avoid anxiety, depression and other bad emotions.