Similar decrease of proliferation employing Ki-67 after brief neoadjuvant hormonal treatment on invasive ductal carcinoma versus invasive lobular carcinoma.

Abstract

e12606 Background: Invasive lobular carcinoma (ILC) differs from the more prevalent invasive ductal carcinoma (IDC) in histology, molecular underpinning, and biological responsiveness to cytotoxics. Patients diagnosed with IDC or ILC were evaluated in the clinical setting to determine if they differ in responsiveness to neoadjuvant hormone treatment. Methods: This is a retrospective observational study of an underserved, low income, rural population in Oroville, California. The data for this study was collected over ten years (2011-2021) from 58 estrogen receptor positive (ER+) breast cancer patients. The majority of these patients (48/58) were diagnosed with IDC with ages ranging from 35 to 91 (mean age is 66) and the remaining 10 were diagnosed with ILC with ages ranging from 58 to 85 (mean age is 64). Patients were given neoadjuvant hormone treatment starting after their initial biopsy confirming ER+ status until scheduled surgical removal by lumpectomy or mastectomy. Ki-67 was measured prior to treatment and then measured again after a minimum of 14 days on hormone therapy. The initial Ki-67 range for patients with IDC was 2%-75% (median of 15%). Ki-67 initial range for patients with ILC was 2%-30% (median of 11%). Positive response to treatment was set at > 50% reduction in Ki-67, with no response set at < 50% reduction in Ki-67. We compared the response rates of ILC and IDC patients using a chi-square test. Results: Chi-square analysis found no statistically significant difference between IDC and ILC response to hormone therapy. 34/48 (71%) patients with IDC responded to treatment, and 8/10 (80%) of ILC patients showed response. Incidentally, we noticed a higher prevalence of ILC in our community compared to expected numbers. Conclusions: When evaluating hormone therapy responsiveness in the neoadjuvant setting, there is no observable statistical difference in response rates between IDC and ILC. Neoadjuvant hormone testing employing Ki-67 response identifies subgroups of patients who benefit from the addition of new biologics (-ciclibs, mTOR inhibitors) in addition to hormone treatment. Our experience supports testing in this way to further individualize the care of patients unable to participate in clinical trials.