Clinical characteristics and treatment outcomes of invasive ductal and lobular carcinoma: analyses of 54,832 taiwan cancer registry index cases.

PURPOSE: Invasive lobular cancer (ILC) is the second most common histology type of breast cancer followed by invasive ductal carcinoma (IDC). This study aimed to investigate the characteristic, treatment strategies, and clinical outcomes of ILC based on a national population-based cancer registry. METHODS: This study recruited 2671 ILC and 52,215 IDC patients diagnosed between 2011 and 2017 using the Taiwan Cancer Registry (TCR). Correlations between ILC and IDC subgroups were assessed using 1:4 propensity score matching and compared using the χ2 test. Disease free survival(DFS) and overall survival(OS) were estimated using the Kaplan-Meier method with the log-rank test. The risk of disease relapse and mortality were assessed using Cox proportional hazards model. RESULTS: ILC patients had larger tumor sizes, more positive axillary lymph node involvement, lower tumor grade, and higher cancer stage than IDC patients. After matching, ILC patients had a significantly higher rate of receiving mastectomy (58.93% and 53.85%) and positive surgical margin regardless of surgery type. ILC exhibited a significantly higher rate of distant metastasis than IDC(3.67% and 2.93%), but no difference in local recurrence rate, DFS or OS between the two groups. Higher cancer stage, higher grade, and mastectomy were risk factors for disease relapse and cancer-specific mortality. The hormone receptor-positive and HER2 over-expression subtypes were found to be associated with a reduced risk of disease relapse, while only PR positivity was associated with a decreased risk of mortality. (all P-values < 0.05). CONCLUSION: ILC patients had a higher mastectomy rate, higher surgical margin rate and distant metastasis rate than IDC patients. There is no significant difference in DFS or OS between ILC and IDC patients. Mastectomy was associated with poor outcomes regardless of ILC or IDC.