Similar decrease of proliferation employing Ki-67 after brief neoadjuvant
hormonal treatment on Invasive Ductal Carcinoma versus Invasive Lobular
Carcinoma.
Martin Majer, Elizabeth Fauchier Little, Sarah Jones
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.