E94: Neoadjuvant Hormonal Therapy in Invasive Ductal vs Lobular Carcinoma of the Breast: A Comparative Analysis

Introduction: Research has shown that patients with invasive lobular carcinoma (ILC) of the breast are more likely to receive a mastectomy and less likely to be downstaged with neoadjuvant intravenous chemotherapy when compared to patients with invasive ductal carcinoma (IDC). Hormonal therapy is often administered in the neoadjuvant setting for breast cancer but may be underutilized as differences in histologic response to neoadjuvant hormonal therapy are not clearly understood. Therefore, we aimed to investigate differences in clinical response by histologic subtype to neoadjuvant hormonal therapy.

Methods: The National Cancer Database (NCDB) was used to identify women with IDC and ILC who underwent neoadjuvant hormonal therapy in the absence of neoadjuvant chemotherapy between 2004-2020. Clinical and pathological T-staging were examined and patients with clinical T2 lesions or greater that downstaged prior to surgery were identified and comparisons of response by histologic subtype type were made using univariate and multivariate analyses. The effect of duration of neoadjuvant hormonal therapy was also examined in each cohort.

Results: A total of 8,013 patients from NCDB met inclusion criteria for this cohort. Among women with IDC (5,758; 71.9%), 2,275 (39.5%) patients had lesions that downstaged. Among women with ILC (2,255; 28.1%), 674 (29.9%) patients had lesions that downstaged. The difference in response to neoadjuvant hormonal therapy by histologic subtype was found to be statistically significant (p< 0.001). Downstaging by clinical T stage with neoadjuvant hormonal therapy is shown in Figure 1. Overall, the duration of neoadjuvant hormonal therapy was longer in patients with downstaged lesions compared to those that did not downstage (mean = 126.8 v 99.4 days; p< 0.001). This relationship held true for both IDC (mean = 124.2 v 97.6 days; p< 0.001) and ILC (mean = 135.7 v 103.4 days; p< 0.001).

Conclusions: Overall, ILC lesions are less likely to downgrade after neoadjuvant hormonal therapy alone compared to IDC lesions. Additionally, both histologic subtypes were more likely to clinically downgrade after receipt of at least 120 days of neoadjuvant hormonal therapy. Therefore, we conclude that neoadjuvant hormonal therapy alone demonstrates decreased efficacy in ILC when compared to IDC, and may contribute to higher mastectomy rates in this group. This efficacy may increase with duration of therapy. Surgeons can use this information to aid in surgical decision making when counseling patients with breast cancer.