Breast benign papillary lesions are divided into intraductal papilloma (IDP), radial sclerosing lesions (RSL), subareolar sclerosing duct hyperplasia, cystic and papillary apocrine metaplasia, florid papillomatosis of the nipple, syringomatous adenoma of the nipple and others. Breast benign papillary lesions are many but most common and important lesion is IDP. And accurate diagnosis of IDP from malignancy is important.

Clinically, IDP demonstrate nipple discharge. Hence Core Needle Biopsy (CNB) is done in suspected IDP. However in the CNB specimen, sometimes it is difficult to determine benign or malignant. In these cases, myoepithelial marker of p63 and calponin are useful. And also high-molecular-weight cytokeratins of CK5/6 and CK14 are helpful staining.

Here, in relation to IDP, we would like to present new concept of two papillary lesions at a glance IDP. In the past, lacking myoepithelial cells is thought to be invasion and means malignancy. Two cases of 68- (Case1) and 44-year-old (Case2) female are presented. They have abnormality in the breast. And they came to our hospital for further examination and treatment. Radiologically, malignancy could not completely excluded. Then, breast excision was performed. Histologically, both cases revealed papillary neoplastic lesions lined by fibrovascular core and nuclear inverse-polarity without atypia. Loss of myoepithelial cells was observed by HE, p63, and calponin. Previous report indicate CK5/6, ER, p63 and MUC3 are important for distinguishing between papillary lesions according to the differential index (based on Allred score) of ([ER total score] + [MUC3 total score])/([CK5/6 total score] + [p63 total score] + 1). Based on this analysis, our 2 cases had benign lesions. Additionally, the Ki-67 index was <1% in both cases, and no evidence of disease was observed minimum 62 months of follow-up for both cases, despite lack of additional treatment. Thus, we propose that lack of myoepithelial cells in papillary lesions do not necessarily indicate malignancy and thought to be benign. These lesions are reported and named “Nuclear inverse polarity papillary lesion lacking myoepithelial cells”. However, the name is too long and its distinctiveness, someone think this tumor as “Tajima tumor” as for the advocator.