Before we talk about the relationship between mastocytosis and breast cancer, let’s first understand a concept, namely precancerous lesions. According to pathology, precancerous lesions are those that appear before malignant tumors and have some degree of morphological atypical hyperplasia, but do not yet have malignant characteristic changes, or are considered to be more likely to develop into cancer. Some people include any lesions that may develop into cancer as precancerous lesions, regardless of their likelihood and time to cancer, without restriction, such as breast hyperplasia, chronic cervicitis, chronic ulcers, etc. Currently, this view is considered too generalized and lacks practical value. From the definition of precancerous lesions, it can be seen that the so-called precancerous lesions are atypical hyperplasia, regardless of any organ or lesion, and only when they reach atypical hyperplasia are they classified as precancerous lesions. Atypical hyperplasia is a necessary stage in the process of carcinogenesis, which is a continuous process of spectrum (i.e. normal → hyperplasia → atypical hyperplasia → carcinoma in situ → infiltrating carcinoma). Under the continuous effect of certain factors, this stage can change from quantitative to qualitative and become a malignant tumor, while in other cases, it is reversible and recoverable. It can be seen that precancerous lesions are by no means all necessarily transformed into cancer, but only more likely to develop into cancer, which is conditional and sometimes can be stagnant for a long time. Pathology usually classifies atypical hyperplasia into three grades, i.e. mild, moderate and severe. This grading is appropriate for tumors of different origins in various tissues, especially those of epithelial origin. Generally speaking, mild atypical hyperplasia has little chance of becoming cancerous, while severe atypical hyperplasia is more likely to become malignant, and the differential diagnosis with cancer is more difficult, so special clinical attention should be paid to make appropriate treatment.