The texture of breast nodules has always the focus of clinical palpation,and the stiffness of breast nodules has been a hot research topic of ultrasound elastography. Both texture and stiffness are based on the principle that malignant tissue is stiffer than benign tissues,but the underlying mechanisms of breast nodule stiffness is not yet confirmed. Breast nodule stiffness is affected by both substance and mesenchyme,and the latter is an important factor. Collagen,as the major composition of the extra cell matrix,plays an important role in breast nodule stiffness. This review summarizes the molecular mechanisms of intracellular and extracellular changes in the formation of breast nodules.