E. C. Shenvi1, J. Murphy1, R. Sarkar1, S. Blair1 1University Of California – San Diego,San Diego, CA, USA
Introduction: Invasive lobular carcinomas (ILC) represent a minority of HER2-positive breast cancers, and may respond differently to systemic treatment. We investigated if lobular histology was associated with breast conservation rates and response to neoadjuvant therapy.
Methods: Using the National Cancer Database (NCDB) for years 2006-2015, we selected patients with invasive breast cancer and Her2 positivity. Rates of mastectomy and response to neoadjuvant therapy were examined as a function of histology by logistic regression controlling for demographics and tumor characteristics. Statistical analysis was done in R.
Results: There were 142,909 patients in the NCDB with invasive Her2-positive carcinomas, of which 126,702 had ductal and 4,887 had lobular histology. ILC was associated with an OR of 1.34 for ultimately having a mastectomy instead of breast conservation (95% confidence interval[CI] 1.23-1.46 p<<0.001) among those treated surgically. Pathologic response to neoadjuvant therapy was available for only 28,196 subjects. Lobular histology had lower rates of complete response to neoadjuvant systemic therapy, with OR of 0.81 (95% CI 0.68 – 0.97, p=0.022)., any response to neoadjuvant therapy OR of 0.65 (95% CI 0.47 – 0.92, p=0.012). Among patients given chemotherapy, lobular histology was again associated with increased rates of mastectomy, OR 1.34 (95% confidence interval 1.22-1.46, p<<0.001) controlling for clinical stage and patient demographics. Mortality data in this subset was available for 106,288 patients. Lobular histology was associated with increased mortality, OR 1.24 (1.09-1.42, p=0.001. This effect persisted when controlling for surgical treatment, OR 1.23 (1.07-1.42, p=0.003).
Conclusion: Her2-Neu positive ILC represents a small minority of breast cancers. It appears to have an intermediate response to neoadjuvant therapy compared to Her2-neu positive IDC, which is known to have high pathologic complete response rates. Clinicians should use this data when counseling patients on treatment options and appropriate expectations for surgical treatment.