Differential Prognostic Impact of Strong PD-L1 Expression and 18F-FDG Uptake in Triple-negative Breast Cancer

Objectives: Triple-negative breast cancers (TNBC) is an aggressive disease and often associated with early distant metastases, which negate the role of adjuvant radiotherapy. We studied the clinical utility of programmed death ligand-1 (PD-L1) and other available factors in predicting clinical outcome in TNBC. Methods: Of the 539 patients with newly diagnosed TNBC between 2004 and 2011, we analyzed 117 patients who had both tumor samples which PD-L1 protein expression could be evaluated using immunohistochemistry and initial staging 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) data to find available immunologic or metabolic factors. Median follow-up duration was 53 months. Results: Strong PD-L1 expression was significantly associated with increased risk of recurrence along with tumor hypermetabolism. The systemic recurrence rate was significantly higher in the strong PD-L1 group than the weak PD-L1 group (35% vs. 11%; P=0.002); whereas there was no difference in locoregional failures (8% vs. 8%). Meanwhile, tumor hypermetabolism seemed to relate with an increase in overall recurrences (26% vs. 8%; P=0.019), not with specific type (locoregional, 9% vs. 3% [P=0.289]; systemic, 22% vs. 8% [P=0.051]). The relationship between PD-L1 expression and survival outcomes retained significance even after adjusting potential risk factors. Conclusions: PD-L1 and tumor metabolism might have role of predicting an increase in treatment failures. Especially, strong PD-L1 expression status was related to distant metastasis-dominant recurrence pattern which needs for intensive systemic therapy.