Treatment patterns and outcomes in invasive lobular versus ductal breast carcinoma: A real-world analysis.

e12665 Background: Invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC) differ in tumor biology; however, current clinical guidelines frequently recommend similar treatment strategies. Real-world comparative data across the full spectrum of disease stages remain limited. We compared clinicopathologic characteristics, treatment patterns, and outcomes between ILC and IDC in a real-world cohort. Methods: We conducted a retrospective cohort study of adults with invasive breast carcinoma treated at a tertiary cancer center in Colombia. Tumors were classified as ILC or IDC, and patients across all clinical stages were included. Clinicopathologic features, treatment patterns, and survival outcomes were compared between groups. Results: A total of 209 patients were included, of whom 31 (14.8%) had ILC and 178 (85.2%) had IDC. Median age was 56.3 years (IQR 46.3–66.0) in the ILC group and 58.0 years (IQR 51.8–67.6) in the IDC group. ILC tumors demonstrated lower proliferative activity, with a significantly lower median Ki-67 (10.0% [IQR 5.0–20.0] vs 27.5% [IQR 15.0–50.0], p < 0.001). Neoadjuvant therapy was less frequently administered in ILC compared with IDC (6.5% vs 32.6%, p = 0.007), while upfront surgery was more common (90.3% vs 62.4%, p = 0.009). Use of adjuvant therapy was similar between groups (87.1% in both). After a median follow-up of 55.6 months, overall survival (OS) and progression-free survival (PFS) were comparable between histologic subtypes. Median OS was 55.9 months for ILC and 55.1 months for IDC, and median PFS was 49.8 and 51.9 months, respectively (p > 0.9). These survival estimates should be interpreted in the context of a limited number of events. Conclusions: In this real-world cohort, ILC exhibited distinct biologic features and treatment patterns compared with IDC, including lower proliferative activity and less frequent use of neoadjuvant therapy, without observed differences in survival outcomes. These findings underscore the importance of considering histologic subtype in therapeutic decision-making and trial design. Baseline clinicopathologic characteristics by histologic subtype. Variable Overall cohort (n=209) Invasive ductal carcinoma (n=178) Invasive lobular carcinoma (n=31) Age in years, median (IQR) 58.2 (52-68) 56,3 (46-66) 58,0 (51,8-67,6) ER positive, n (%) 167 (79.9%) 137 (77.0%) 30 (96.8%) HER2 3+, n (%) 31 (14.8%) 31 (17.4%) 0 (0.0%) Ki-67, median (IQR) 25 (10- 50) 27.5 (15-50) 10 (5-20) Histologic grade 3, n (%) 57 (27.3%) 54 (30.3%) 3 (9.7%) Classic LCIS, n (%) 9 (4.3%) 1 (0.6%) 8 (25.8%) AJCC stage (I–II vs III–IV), n (%) 145 (69.4%) vs 44 (21.1%) 126 (70.8%) vs 39 (21.9%) 19 (61.3%) vs 5 (16.1%) OS, months (IQR) 55.6 (38.8-77.4) 55.1 (40.5-76.1) 55.9 (9.0-88.5) PFS, months (IQR) 51.3 (34.0-75.6) 51.9 (35.3-74.9) 49.8 (9.0-82.3)