Establishment of risk prediction nomogram for ipsilateral axillary lymph node metastasis in T1 breast cancer.

:To establish and verify a risk prediction nomogram for ipsilateral axillary lymph node metastasis in breast cancer stage T1 （mass ≤ 2 cm）. :The clinicopathological data of 907 patients with T1 breast cancer who underwent surgical treatment from January 2010 to June 2015 were collected，including 573 cases from the Second Affiliated Hospital of Zhejiang University School of Medicine （modeling group） and 334 cases from Zhejiang University Lishui Hospital （verification group）. The risk factors of ipsilateral axillary lymph node metastasis were analyzed by univariate and multivariate logistic regression. The influencing factors were used to establish a nomogram for predicting ipsilateral axillary lymph nodes metastasis in T1 breast cancer. The model calibration，predictive ability and clinical benefit in the modeling group and the verification group were analyzed by C index，receiver operating characteristic curve，calibration curve and decision curve analysis （DCA） curve，respectively. :Univariate analysis showed that lymph node metastasis was related with primary tumor size，vascular tumor thrombus，Ki-67，histopathological grade，and molecular type （<0.05 or <0.01）. Multivariate logistic regression analysis showed that the primary tumor > vascular tumor thrombus，Ki-67 positive，estrogen receptor （ER） positive，and histopathological grade 2-3 were independent risk factors of axillary lymph node metastasis （<0.05 or <0.01）. Based on the independent risk factors，a nomogram prediction model was established. The C indexes of the model group and the validation group were 0.739 （95%:0.693-0.785） and 0.736 （95%:0.678-0.793），respectively. The calibration curve and DCA curve of the modeling group and the verification group indicated that the model was consistent and had good clinical benefit. :Primary tumor size，histopathological grade，vascular tumor thrombus，Ki-67，and ER status are predictors of ipsilateral axillary lymph node metastasis in T1 breast cancer. The established prediction nomogram can effectively predict the risk of ipsilateral axillary lymph node metastasis in T1 breast cancer，which can be used as a reference for individualized axillary management.