Pathologic complete response after neoadjuvant chemotherapy in triple-negative invasive lobular carcinoma: A meta analysis.

Abstract

e12681 Background: Triple-negative invasive lobular carcinoma (TN-ILC) is a rare TNBC subtype with limited evidence to guide systemic therapy. Neoadjuvant chemo-immunotherapy is standard for stage II–III TNBC, yet expected pathologic complete response (pCR) rates in TN-ILC remain unclear. Given the distinct biology and lower chemosensitivity of ILC, we performed a systematic review and meta-analysis to define pCR rates in TN-ILC. Methods: We conducted a systematic review of studies reporting pCR in patients with TN-ILC treated with neoadjuvant systemic chemotherapy. PubMed, Cochrane Library, and Web of Science were searched, with manual review of ASCO and ESMO abstracts, through January 23, 2026. Pooled pCR estimates were calculated using logit-transformed random-effects models, excluding single-case reports and studies with < 2 TN-ILC patients. Heterogeneity was assessed using I², and survival outcomes were summarized descriptively due to inconsistent reporting. Results: Of 68 studies identified, 5 met inclusion criteria; two large registry-based neoadjuvant cohorts comprising 425 TN-ILC patients contributed to the pooled analysis. Study-level pCR rates ranged from 20.5% to 23.2%. The pooled pCR rate following neoadjuvant chemotherapy was 22.5% (95% CI: 18.8-26.7%) with no observed heterogeneity (I² = 0%). Details regarding survival outcomes, CT regimens, including anthracycline use, platinum exposure, and incorporation of IO, were variably reported and could not be analyzed quantitatively. Conclusions: Approximately one in five patients with TN-ILC achieve pCR following neoadjuvant CT, supporting the use of neoadjuvant systemic therapy despite limited representation of this rare histologic subtype in prospective trials. However, these pCR rates are lower than those reported in contemporary unselected TNBC cohorts treated in prospective studies. Importantly, most available TN-ILC–specific evidence predates the routine incorporation of IO, which is now standard in early-stage TNBC; therefore, the magnitude of benefit from CT-IO in TN-ILC remains unknown and represents a key limitation of this analysis. Future registry-based analyses including survival outcomes, molecular characterization, and standardized TN-ILC–specific reporting within modern CT-IO trials are needed to better define optimal treatment strategies for this rare subtype. pCR Outcomes in TN-ILC with neoadjuvant chemotherapy. Group / Study TN-ILC (n) pCR (n/N) pCR %, 95% CI Pooled estimate (primary) 425 95/425 22.5 (18.8-26.7) Joshi et al., 2023 298 69/298 23.2 (18.7-28.3) Riba et al., 2019 127 26/127 20.5 (14.4-28.3) Case reports† 4 2/4 50.0 (15.0-85.0) †Case reports are summarized descriptively and were not included for statistical inference.