Objective To explore the clinicopathological features of micropapillary pure mucinous carcinoma (MPPMC) and MPPMC combined with invasive micropapillary carcinoma (IMPC). Methods Clinical pathological data of 8 cases of MPPMC and 5 cases of MPPMC combined with IMPC were collected and the histological morphology, immune phenotypes, and clinical features were analyzed. Results Transitional regions were observed in 5 cases of MPPMC combined with IMPC. The mucus around the micropapillary gradually disappeared and formed IMPC. The expression of Ki-67 in cancer tissues significantly increased after the transformation of MPPMC to IMPC. The rate of lymph node metastasis of the MPPMC group was only 12.5%, while that of the MPPMC combined with IMPC group was 80%. The main type of cancer in lymph node metastases was IMPC. Conclusion Breast MPPMC and IMPC may be in the same tumor lineages. The biological behavior of MPPMC combined with IMPC is more serious. The treatment of MPPMC combined with IMPC should reference that of IMPC.