Dear Editor

I read the Adachi et al. study [1], in which they analyzed the prognosis of invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC) in each subtype and examined the effectiveness of adjuvant chemotherapy in luminal ILC. They concluded that luminal ILC had a poorer prognosis than luminal IDC, contributing to the worse prognosis of ILC than that of IDC in the overall cohort. However, the authors did not describe whether mixed invasive ductal lobular carcinoma (mDLC) cases were excluded or not. mDLC remains a poorly understood subtype of breast cancer composed of coexisting ductal and lobular components.These cases might show different clinical and pathological characteristics other than pure ILC [2,3,4,5]. One study investigated clinicopathologic characteristics and determine whether mDLC is clinically more similar to IDC or ILC. They observed a higher concordance in clinicopathologic characteristics between mDLC and ILC, compared to IDC [6]. Another study examined a well-characterised series of breast carcinoma with a long term follow-up that comprised 140 mDLC, 2170 IDC and 380 pure ILC. They reported that mDLC showed an association with higher grade, positive LN metastasis, VI and development of regional metastasis when compared to pure ILC [7]. In conclusion, more research is necessary to fully understand the biology and clinical importance of tumors containing mDLC, which are less frequent.