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Long-term Outcomes of Slowly Proliferating Luminal A-like Invasive Lobular Carcinoma Versus Invasive Carcinoma of No
Dahn Byun1, Ji Won Yoo1, Jihoon Lee1
1Division of Breast Surgery, Department of Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Purpose:
Long-term outcome comparisons between invasive lobular carcinoma (ILC) and invasive carcinoma of no special type (NST, historically referred to as invasive ductal carcinoma) remain inconsistent, particularly in patients with low-proliferative hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) disease. This study evaluated the long-term outcomes of ILC and NST in a pathologically defined, low-proliferative, HR+/HER2- (luminal A-like) cohort.
Methods:
This retrospective, single-institution study included patients with HR+/HER2- breast cancer and Ki-67 ≤ 20% who underwent surgery between 2008 and 2015. Patients with mixed histopathology, those who underwent palliative surgery, or those who received neoadjuvant chemotherapy were excluded. Survival was analyzed using the Kaplan-Meier method and multivariable Cox regression. A secondary 24-month landmark analysis included patients who were alive, disease-free, under observation, and receiving endocrine therapy 24 months after surgery.
Results:
Among 3,439 patients, 3,156 had NST and 283 had ILC. Compared with NST, ILC was associated with a higher rate of synchronous bilateral breast cancer, a more advanced pathological stage, and a lower nuclear grade. In the comprehensive cohort, breast cancer-specific survival did not differ significantly (log-rank p = 0.081), whereas disease-free survival (DFS) and distant metastasis-free survival (DMFS) were worse in patients with ILC (log-rank p < 0.001 and p = 0.005, respectively). After adjustment for measured clinicopathological factors, these differences were no longer statistically significant (DFS: adjusted hazard ratio [HR], 1.27; 95% confidence interval [CI], 0.91-1.79; p = 0.164; DMFS: adjusted HR, 1.38; 95% CI, 0.83-2.30; p = 0.210). Detailed biomarker analyses showed similarly high estrogen receptor expression in both groups and lower exact Ki-67 values in ILC. The 24-month landmark analysis revealed the same overall pattern.
Conclusion:
In this low-proliferative HR+/HER2- cohort, ILC showed less favorable unadjusted long-term DFS and DMFS than NST, but these differences were attenuated and were no longer statistically significant after adjustment for measured clinicopathological characteristics.
