Effect of Neoadjuvant Hormonal Therapy on Breast Conservation in Invasive Ductal Versus Lobular Carcinoma of the Breast: A Comparative Analysis.

Background: Comparative efficacy of neoadjuvant hormonal therapy in downstaging invasive ductal carcinoma (IDC) versus invasive lobular carcinoma (ILC) remains an area of uncertainty and may impact primary breast conservation rates.

Methods: The National Cancer Database was used to identify women with IDC and ILC who underwent neoadjuvant hormonal therapy alone between 2004 and 2020. Clinical and pathological T-staging were examined and patients that downstaged before surgery were identified. Univariate and multivariate comparison analyses were performed. The effect of duration of neoadjuvant hormonal therapy was also examined.

Results: Among women with IDC, 39.5% had lesions that downstaged compared to 30.0% with ILC (p < 0.001). Overall, the duration of neoadjuvant hormonal therapy was longer in patients with downstaged lesions compared to those that did not (mean = 126.9 v 99.4 days; p < 0.001). Of those who downstaged, 43% of patients with IDC and 57.8% of patients with ILC underwent mastectomy following neoadjuvant hormonal therapy.

Conclusions: Overall, ILC lesions are less likely to downstage after neoadjuvant hormonal therapy alone compared to IDC lesions. In both histologic subtypes, cancers were more likely to downstage after over 120 days of neoadjuvant hormonal therapy. Clinicians should be mindful when counseling patients that neoadjuvant hormonal therapy alone may not preclude the need for mastectomy in ILC.