Triple-negative breast cancer (TNBC) accounts for approximately 15%-20% of breast cancers diagnosed worldwide, which amounts to almost 200 000 cases each year. Although historically TNBC is considered difficult to treat with a poor prognosis, there is emerging evidence showing excellent response rates in a subset of TNBC patients. Attempts to de-escalate chemotherapy in hormone-receptor-positive (HR+) and HER2-neu amplified breast cancer subtypes have been successful. At present, robust strategies to personalize therapy in early-stage TNBC do not exist, and despite excellent response rates in a subset of patients, all patients are exposed to the same several cycles of cytotoxic chemotherapy. Personalizing therapy in TNBC represents a challenge due to the scarcity of treatment options outside of cytotoxic chemotherapy and limited predictive and prognostic biomarkers to tailor treatment. Recent developments in understanding TNBC biology have sparked interest in exploring treatment optimization and personalization with the goal of achieving excellent response rates and long-term clinical outcomes, while simultaneously reducing physical, psychological, and financial toxicities for select patients. Here, we provide an update on the current evidence to support future studies examining de-escalating chemotherapy in patients with low-risk TNBC and adjuvant intensification strategies to improve outcomes for patients who are at high risk for systemic failure despite current standard-of-care treatments.

High stromal tumor-infiltrating lymphocytes (sTILs) are associated with improved pathologic complete response (pCR) in triple-negative breast cancer (TNBC). We hypothesize that integrating high sTILs and additional clinicopathologic features associated with pCR could enhance our ability to predict the group of patients on whom treatment de-escalation strategies could be tested. In this prospective early-stage TNBC neoadjuvant chemotherapy study, pretreatment biopsies from 408 patients were evaluated for their clinical and demographic features, as well as biomarkers including sTILs, Ki-67, PD-L1 and androgen receptor. Multivariate logistic regression models were developed to generate a computed response score to predict pCR. The pCR rate for the entire cohort was 41%. Recursive partitioning analysis identified ≥20% as the optimal cutoff for sTILs to denote 35% (143/408) of patients as having high sTILs, with a pCR rate of 59%, and 65% (265/408) of patients as having low sTILs, with a pCR rate of 31%. High Ki-67 (cutoff > 35%) was identified as the only predictor of pCR in addition to sTILs in the training set. This finding was verified in the testing set, where the highest computed response score encompassing both high sTILa and high Ki-67 predicted a pCR rate of 65%. Integrating Ki67 and sTIL may refine the selection of early stage TNBC patients for neoadjuvant clinical trials evaluating de-escalation strategies.

High stromal tumor-infiltrating lymphocytes (sTILs) are associated with an improved pathologic complete response (pCR) and survival in triple-negative breast cancer (TNBC). We hypothesized that high baseline sTILs would have a favorable prognostic impact in TNBC patients without a pCR after neoadjuvant chemotherapy (NACT). In this prospective NACT study, pretreatment biopsies from 318 patients with early-stage TNBC were evaluated for sTILs. Recursive partitioning analysis (RPA) was applied to search for the sTIL cutoff best associated with a pCR. With ≥20% sTILs identified as the optimal cutoff, 33% patients had high sTILs (pCR rate 64%) and 67% had low sTILs (pCR rate 29%). Patients were stratified according to the sTIL cutoff (low vs. high) and response to NACT (pCR vs. residual disease (RD)). The primary endpoint was event-free survival (EFS), with hazard ratios calculated using the Cox proportional hazards regression model and the 3-year restricted mean survival time (RMST) as primary measures. Within the high-sTIL group, EFS was better in patients with a pCR compared with those with RD (HR 0.05; 95% CI 0.01–0.39; p = 0.004). The difference in the 3-year RMST for EFS between the two groups was 5.6 months (95% CI 2.3–8.8; p = 0.001). However, among patients with RD, EFS was not significantly different between those with high sTILs and those with low sTILs (p = 0.7). RNA-seq analysis predicted more CD8+ T cells in the high-sTIL group with favorable EFS compared with the high-sTIL group with unfavorable EFS. This study did not demonstrate that high baseline sTILs confer a benefit in EFS in the absence of a pCR.

The KEYNOTE-522 (KN522) regimen for neoadjuvant treatment of triple negative breast cancer (TNBC) utilized q3week dosing for doxorubicin plus cyclophosphamide (AC); however, dose-dense AC (ddAC) has demonstrated superior overall survival (OS) compared to q3week AC in anthracycline and taxane-based regimens. We performed a retrospective analysis assessing the use of ddAC in KN522 and the impact of sequencing ddAC before or after carboplatin/paclitaxel (CbT) plus pembrolizumab on multiple outcomes. 128 patients with TNBC were included. Overall pathologic complete response (pCR) rate of 56%. Sequencing of ddAC vs CbT first showed no difference in pCR rate (ddAC 55% vs. CbT 58%, p = 0.77). However, ddAC first compared to CbT first correlated with a significant increase in the incidence of overall treatment delays (ddAC 70% vs. CbT 51%, p = 0.03), with cytopenias most frequent (ddAC 59% vs. CbT 31%, p = 0.001). ddAC in a modified KN522 regimen is safe, tolerable, and effective. Efficacy is comparable regardless of chemotherapy sequencing, but ddAC first is significantly associated with higher rates of treatment delays and cytopenias.

Metaplastic breast cancer (MpBC) treated with standard chemotherapy has low rates of complete pathological response (pCR)(2–23%). In this study, we evaluate the response to neoadjuvant chemo-immunotherapy (NACI) in early-stage MpBC. Thirty-two stage I-III MpBC patients treated with NACI (KEYNOTE-522 regimen) were prospectively enrolled in an institutional rare tumor program. All MpBC were triple negative; most were of chondromyxoid/matrix-producing (12/32, 38%). The majority had stage II (78%) tumors, 12/32 (37.5%) patients completed NACI, 11/32 (34%) progressed during NACI, and in the remaining 9, NACI was discontinued due to side effects. The pCR rate in the entire cohort was 22% (7/32) and it was statistically higher (5/8, 62%) among patients with high ( ≥ 60%) stromal tumor-infiltrating lymphocytes (sTILs) as compared to patients with < 60% sTILs (1/11, 9%). Most patients received adjuvant systemic therapy (capecitabine 16/32, pembrolizumab 20/32). At a median follow-up of 13 months, there were a total of 2 local recurrences, 10 distant recurrences, and 7 deaths. We demonstrated a modest pCR rate in MpBC with the addition of pembrolizumab (22%). Nonetheless, amongst patients with high sTILs, high pCR rates—comparable to those in the KEYNOTE-522 trial—were observed. These findings suggest that sTILs can be used to triage MpBC patients for NACI.