L. A. Riba1, T. L. Russell1, T. A. James1 1Beth Israel Deaconess Medical Center,Surgery,Boston, MA, USA
Introduction: The achievement of pathological complete response (pCR) following neoadjuvant chemotherapy (NCT) for breast cancer is associated with improved survival and enables the use of more conservative surgical management. Invasive lobular carcinoma (ILC) has been extensively shown to have a lower response rate to NCT than invasive ductal carcinoma (IDC). The purpose of this study is to summarize the national trends in the use of NCT for ILC, to characterize the overall pCR in ILC patients compared to IDC patients, and to determine if there is a subset of patients with ILC who show improved pCR rates.
Methods: This is a retrospective study using data from the National Cancer Database. The population consisted of female patients with clinical T1-T4 primary ILC or IDC diagnosed and treated between 2010 and 2014. For patients receiving NCT, the event of pCR was assessed by using the variable ‘Response to Neoadjuvant Therapy’, and each patient was categorized as either presenting with pCR or not. Clinically relevant variables, including age, TNM stage, tumor grade and tumor receptor status, were used in multivariate logistic regression models for each histologic subtype, modeling for the event of pCR. From the multivariate regression model we obtained odds ratios and 95% confidence intervals (CI) for each variable as a predictor for pCR in either ILC or IDC cases.
Results: Our study population consisted of 387,200 women, of which 89.47% had IDC and 10.53% had ILC. Patterns of systemic therapy varied significantly between the two histologic subtypes with NCT being used in 15.39% of the IDC cases and only in 8.57% of the ILC cases. A significantly higher rate of pCR was found in the cases of IDC compared to those of ILC (22.8% compared to 8.08%; p < 0.0001). Multivariate logistic regression analysis found a significant relationship between increased rates of pCR in lobular carcinoma with HER2-positive subtypes (OR, 11.309; 95% CI, 6.812-18.777) and TNBC cases (OR, 4.484; 95% CI, 2.924-6.876). Patients with older age (OR, 0.273; 95% CI, 0.075-0.999) were seen to have significantly lower response rates in the ILC group.
Conclusion: From a treatment response standpoint, the use of NCT in women with ILC has not been proven widely beneficial. While complete response to NCT in patients with ILC is unusual, patients with HER2 positive and triple negative disease demonstrate pCR rates comparable to those found in cases of IDC. Our findings demonstrate selective benefit from NCT in the treatment of ILC, specifically restricted to those patients presenting with HER2-positive tumors or TNBC.