Dear editor

I read with great interest the article by de Thill et al. [1] in which they presented prospective real-world data of patients with metastatic invasive lobular cancer (mILC) as compared to patients with metastatic invasive ductal cancer (mIDC) receiving systemic therapy in routine care in Germany. They concluded that ILC histopathology was not associated with a better clinical outcome in multivariate analysis, suggesting the need for more tailored treatment strategies for patients with the lobular subtype, despite patients with mILC presenting with some favorable prognostic factors. However, the authors did not describe whether mILC is pure or mixed invasive ductal and lobular carcinoma (IDLC). Because some cases with mILC also carry features of (mIDC), the definition of cases with mILC may be important whether they are pure ILC or mixed IDLC [2]. Furthermore, one study compared the breast cancer patients ILC, IDC and mixed IDLC in terms of clinicopathological and treatment features, metastatic patterns and long-term survival. They suggest that IDLC may have a worse prognosis than IDC and ILC [3]. Taken all together, this issue should be clarified to get better comparison of mILC with mIDC.