Comparison of Invasive Ductolobular Carcinoma and Lobular Carcinoma: An Observational Study

<i>Background and Objectives:</i> Mixed ductolobular carcinomas (mDLCs) are tumors that contain both ductal and lobular components. The clinicopathological characteristics and impacts on survival of the two components, which have distinct biological behaviors, are still not clearly understood. This study aimed to compare the clinicopathological characteristics, recurrence/metastasis patterns, and survival outcomes of mDLC and invasive lobular carcinoma (ILC), as well as to investigate the prognostic significance of both histopathologies. <i>Materials and Methods</i>: The outcomes of 132 patients who were followed and treated between 2010 and 2021 were analyzed. Patients were examined in two groups, ILC and mDLC. Chi-square tests were performed to compare the baseline clinicopathological characteristics and treatments. Survival rates were subsequently analyzed using the Kaplan-Meier method and compared using the Cox proportional hazards model. <i>Results:</i> In this study, 80 (61%) patients had ILC histopathology, while 52 (39%) had mDLC histopathology. Differences between the groups were observed in median age (<i>p</i> = 0.038), N stage (<i>p</i> = 0.046), estrogen receptor (ER) status (<i>p</i> = 0.005), lymphovascular invasion (<i>p</i> = 0.007), median tumor diameter (<i>p</i> = 0.050), and frequency of distant metastasis (<i>p</i> = 0.029). The treatments, relapse patterns, and metastasis patterns were similar (<i>p</i> > 0.05). No differences in overall survival (OS) and disease-free survival (DFS) were observed. In the multivariate analysis, mDLC histopathology was identified as a poor prognostic factor (HR: 2.95, CI 95%: 1.10-7.88, <i>p</i> = 0.030). Histopathology (ILC vs. mDCL) was not identified as a prognostic factor in the Cox regression analysis for DFS. <i>Conclusion:</i> Although mDLC has poor clinicopathological features (younger age, more advanced N stage, more ER negativity, more lymphovascular invasion, and more frequency of metastases) and appears more aggressive than ILC, these changes do not affect survival in this study. However, mDLC histopathology seems to be associated with poor prognosis for OS.