Primary breast diffuse large B-cell lymphoma (DLBCL) is a rare non-Hodgkin's lymphoma with limited data. In this study, a population-based study of primary breast DLBCL in the United States was performed to determine its incidence trends, prognostic factors, survival, the role of surgery as well as the comparison with nodal DLBCL. 1021 patients diagnosed with breast DLBCL were identified in the Surveillance, Epidemiology, and End Results (SEER) cancer registries from 1973-2014. The incidence of both breast and nodal DLBCL increased over time. Patients with breast DLBCL were older, mainly women, diagnosed at earlier stages and had lower prevalence in white and black races compared with nodal DLBCL. Multivariate analysis revealed older age (≥ 70 years old) and advanced stage as independent predictors of worse OS. Independent predictor of better DSS were younger age (< 70 years old), early stage and diagnosis after 2000. When analyzed according to age, stage, race, tumor laterality and year of diagnosis, the overall survival did not benefit from surgery except in patients diagnosed between 2001-2010 and the surgery rate decreased overtime. Compared with nodal DLBCL, breast DLBCL patients exhibited a better outcome. In conclusion, breast DLBCL is a rare tumor with increasing incidence and improved survival over the last four decades. The introduction of rituximab seems to improve the outcome of breast DLBCL. Further studies are needed to advance our understanding of breast DLBCL and optimize the treatment strategy.

Aims The protein expression of programmed death‐ligand 1 (PD‐L1) has been recognised as being a biomarker for poor prognosis in diffuse large B‐cell lymphoma (DLBCL). The aims of this study were to determine PD‐L1 DNA status and mRNA status, and to explore whether they contribute to protein expression and their clinicopathological correlation in DLBCL. Methods and results In this study, we used fluorescence in‐situ hybridisation, RNA in‐situ hybridisation and immunohistochemistry to determine PD‐L1 status at three different levels in 287 DLBCL samples with follow‐up. Their correlation and clinical pathological relevance were also analysed. Our results showed that 1.7% (3/175) of patients had PD‐L1 DNA amplification, 19.9% (57/287) had high PD‐L1 mRNA expression, and 11.8% (34/287) had high PD‐L1 protein expression. Both mRNA and protein expression of PD‐L1 were significantly higher in non‐germinal centre B‐cell‐like (GCB) DLBCL than in GCB DLBCL (P < 0.05). In addition, the patients with high PD‐L1 mRNA or high PD‐L1 protein expression but no PD‐L1 DNA amplification had significantly poorer overall survival (OS) than those with low PD‐L1 expression (P < 0.05). Furthermore, we found that PD‐L1 mRNA and PD‐L1 protein expression were highly correlated (P = 0.012), which was observed in all three samples with DNA amplification. Conclusions PD‐L1 DNA amplification is a rare event, PD‐L1 mRNA is the main contributor to the high PD‐L1 protein expression, and the latter two will serve as important biomarkers for predicting the prognosis of DLBCL patients and selecting them for immunotherapy.

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