To study the pathology, diagnosis and differential diagnosis of papillary carcinoma of the breast featuring expansile invasion.Morphologic analysis and immunohistochemical study using MaxVision method were carried out in 25 cases of papillary carcinoma of the breast featuring expansile type of invasion.All the 25 cases were female, and ranged from 26 to 84 years old in age with median of 69. The diameters of the neoplasms were from 1 cm to 5 cm, among which those of two cases were 4 cm and 5 cm respectively and the others were less than 2.5 cm. The tumor appeared solid and well-demarcated on gross examination. Histologically, the tumor was non-encapsulated. In some cases, the tumor tissue was separated by fibrous septa or intervening native breast tissue. The tumor was composed of arborizing papillae with fibrovascular cores, associated glandular fusion and cribriform pattern. The fibrovascular cores were covered by cuboidal to columnar cells. In 3 of the cases studied, focal transition with micropapillary ductal carcinoma-in-situ was demonstrated. The tumor cells showed mild or moderate degree of nuclear pleomorphism and contained amphophilic to eosinophilic cytoplasm. Mitotic figures were not frequently seen. One case displayed squamous metaplasia and 4 cases showed apocrine metaplasia. Dimorphic features were identified in 2 cases. The stromal tissue within the tumor was often scanty and sometimes sclerotic, associated with various degrees of inflammatory infiltrate and hemosiderin deposition. Immunohistochemical study for smooth muscle actin, p63, CD10 and CK5/6 showed negative staining in all of the 25 cases studied, including the 2 cases with dimorphic features. Seven cases had breast cancer marker study performed. Six cases were positive for estrogen receptor and progesterone receptor. HER2 oncoprotein was not over-expressed in 6 cases. Nine patients underwent axillary dissection and 2 of them showed axillary nodal metastasis.Diagnosis of papillary carcinoma of the breast is one of the most difficult areas in breast pathology. Demonstration of expansile type of invasion, when coupled with complex papillary fusion, cribriform pattern and absence of myoepithelial cells on immunohistochemistry, is helpful in arriving at a correct diagnosis.