Background The H&E stromal tumor-infiltrating lymphocyte (sTIL) score and programmed death ligand 1 (PD-L1) SP142 immunohistochemistry assay are prognostic and predictive in early-stage breast cancer, but are operator-dependent and may have insufficient precision to characterize dynamic changes in sTILs/PD-L1 in the context of clinical research. We illustrate how multiplex immunofluorescence (mIF) combined with statistical modeling can be used to precisely estimate dynamic changes in sTIL score, PD-L1 expression, and other immune variables from a single paraffin-embedded slide, thus enabling comprehensive characterization of activity of novel immunotherapy agents. Methods Serial tissue was obtained from a recent clinical trial evaluating loco-regional cytokine delivery as a strategy to promote immune cell infiltration and activation in breast tumors. Pre-treatment biopsies and post-treatment tumor resections were analyzed by mIF (PerkinElmer Vectra) using an antibody panel that characterized tumor cells (cytokeratin-positive), immune cells (CD3, CD8, CD163, FoxP3), and PD-L1 expression. mIF estimates of sTIL score and PD-L1 expression were compared to the H&E/SP142 clinical assays. Hierarchical linear modeling was utilized to compare pre- and post-treatment immune cell expression, account for correlation of time-dependent measurement, variation across high-powered magnification views within each subject, and variation between subjects. Simulation methods (Monte Carlo, bootstrapping) were used to evaluate the impact of model and tissue sample size on statistical power. Results mIF estimates of sTIL and PD-L1 expression were strongly correlated with their respective clinical assays (p < .001). Hierarchical linear modeling resulted in more precise estimates of treatment-related increases in sTIL, PD-L1, and other metrics such as CD8+ tumor nest infiltration. Statistical precision was dependent on adequate tissue sampling, with at least 15 high-powered fields recommended per specimen. Compared to conventional t-testing of means, hierarchical linear modeling was associated with substantial reductions in enrollment size required (n = 25➔n = 13) to detect the observed increases in sTIL/PD-L1. Conclusion mIF is useful for quantifying treatment-related dynamic changes in sTILs/PD-L1 and is concordant with clinical assays, but with greater precision. Hierarchical linear modeling can mitigate the effects of intratumoral heterogeneity on immune cell count estimations, allowing for more efficient detection of treatment-related pharmocodynamic effects in the context of clinical trials. Trial registration NCT02950259.

Purpose of Review Immunotherapy is emerging as an effective treatment option for metastatic triple-negative breast cancer. In this review, we summarize clinical data of immunotherapy in triple-negative breast cancer and comment on future directions in the field. Recent Findings IMpassion130 was a phase III trial that demonstrated progression-free survival benefit, and potentially overall survival benefit, of first-line chemotherapy (nab-paclitaxel) plus anti-programmed death ligand 1 (PD-L1) atezolizumab, among PD-L1-positive metastatic triple-negative breast cancers. Studies are ongoing to evaluate other combination therapies with immune checkpoint blockade in TNBC, and to evaluate efficacy in PD-L1-negative tumors and in later lines of therapy. Summary Immunotherapy is now a standard option in the treatment of triple-negative breast cancer. Ongoing trials may expand the degree of clinical benefit. Further work is ongoing to identify novel predictive biomarkers, which in the future may enable a personalized approach of combination immunotherapy.

Metaplastic breast cancer is a rare and often chemo-refractory subtype of breast cancer with poor prognosis and limited treatment options. Recent studies have reported overexpression of programmed death ligand 1 (PD-L1) in metaplastic breast cancers, and there are several reports of anti-PD-1/L1 being potentially active in this disease. In this case series, we present 5 patients with metastatic metaplastic breast cancer treated with anti-PD-1-based therapy at a single center, with 3 of 5 cases demonstrating a response to therapy, and one of the responding cases being a metaplastic lobular carcinoma with low-level hormone receptor expression. Cases were evaluated for PD-L1 expression, tumor infiltrating lymphocytes (TILs), DNA mutations, RNA sequencing, and T-cell receptor sequencing. Duration of the response in these cases was limited, in contrast to the more durable responses noted in other recently published reports.

No abstract

1015 Background: Atezolizumab (anti-PD-L1) plus nab-paclitaxel was shown to improve outcomes in mTBNC in a phase III clinical trial. Subjects were required to be > 12 months from curative-intent therapy in this trial. It remains unknown whether non-taxane chemo + anti-PD-1/L1 will be beneficial in mTNBC, or whether this approach is effective in rapidly-progressing patients ( < 12 mo from curative-intent therapy). Methods: mTNBC patients were enrolled in a phase Ib study of anti-PD-1 (pembro, 200mg IV q3w) plus physician’s choice chemo (cape: n = 14, 2000mg BID, 7d on/7d off; or taxol: n = 14, 80mg/m2 q1w). Primary/secondary objectives were to evaluate safety/tolerability (primary) and RECIST1.1 response (w12). The exploratory objective was to explore for differences in immunomodulation according to chemo choice. Mixed effects models were employed to compare the longitudinal effects of chemo on peripheral immune cells (flow cytometry) and T-cell diversity (Immunoseq assay). Results: Enrollment of the trial is complete (n = 28), with 100% of evaluable patients tolerating therapy (n = 22) as of 2/1/2019. Cape ORR was 43% (5 PR, 1 CR, 2 SD) with median PFS = 155d. Taxol ORR was 25% (1 CR, 1 PR, 3 SD) with median PFS = 99d. Subjects enrolled < 12 months from curative-intent therapy had numerically lower response (ORR = 27%, 1 CR, 2 PR, 3 SD) than subjects without rapid progression (ORR = 45%, 1 CR, 4 PR, 2 SD). No significant differences in immunomodulation were observed according to chemo type, however both cape & taxol were associated with declines in T-cell quantity (CD4 p < .02, CD8 p < .04) and Immunoseq T-cell fraction over time. Conclusions: Pembro plus cape or taxol is safe with encouraging efficacy, however activity may be lower in the setting of rapid progression following curative-intent chemo. Cape+pembro efficacy is favorable with no measurable differences in immunomodulation, and therefore cape may be preferred as a chemo backbone in selected patients. Both cape and taxol are associated with iatrogenic declines in T-cell quantity, which may explain the observed dropoff in anti-PD-1/L1 activity in later lines. Clinical trial information: NCT02734290.