Immune checkpoint inhibitor therapies targeting PD-1/PD-L1 are now the standard of care in oncology across several hematologic and solid tumor types, including triple negative breast cancer (TNBC). Patients with metastatic or locally advanced TNBC with PD-L1 expression on immune cells occupying ≥1% of tumor area demonstrated survival benefit with the addition of atezolizumab to nab-paclitaxel. However, concerns regarding variability between immunohistochemical PD-L1 assay performance and inter-reader reproducibility have been raised. High tumor-infiltrating lymphocytes (TILs) have also been associated with response to PD-1/PD-L1 inhibitors in patients with breast cancer (BC). TILs can be easily assessed on hematoxylin and eosin-stained slides and have shown reliable inter-reader reproducibility. As an established prognostic factor in early stage TNBC, TILs are soon anticipated to be reported in daily practice in many pathology laboratories worldwide. Because TILs and PD-L1 are parts of an immunological spectrum in BC, we propose the systematic implementation of combined PD-L1 and TIL analyses as a more comprehensive immuno-oncological biomarker for patient selection for PD-1/PD-L1 inhibition-based therapy in patients with BC. Although practical and regulatory considerations differ by jurisdiction, the pathology community has the responsibility to patients to implement assays that lead to optimal patient selection. We propose herewith a riskmanagement framework that may help mitigate the risks of suboptimal patient selection for immuno-therapeutic approaches in clinical trials and daily practice based on combined TILs/PD-L1 assessment in BC.

The advent of immune-checkpoint inhibitors (ICI) in modern oncology has significantly improved survival in several cancer settings. A subgroup of women with breast cancer (BC) has immunogenic infiltration of lymphocytes with expression of programmed death-ligand 1 (PD-L1). These patients may potentially benefit from ICI targeting the programmed death 1 (PD-1)/PD-L1 signaling axis. The use of tumor-infiltrating lymphocytes (TILs) as predictive and prognostic biomarkers has been under intense examination. Emerging data suggest that TILs are associated with response to both cytotoxic treatments and immunotherapy, particularly for patients with triple-negative BC. In this review from The International Immuno-Oncology Biomarker Working Group, we discuss (a) the biological understanding of TILs, (b) their analytical and clinical validity and efforts toward the clinical utility in BC, and (c) the current status of PD-L1 and TIL testing across different continents, including experiences from low-to-middle-income countries, incorporating also the view of a patient advocate. This information will help set the stage for future approaches to optimize the understanding and clinical utilization of TIL analysis in patients with BC.

BackgroundCyclin D1-positive B cells are occasionally found in the mantle zones of reactive lymphoid follicles, a condition that has been called "in situ mantle cell lymphoma". The clinical significance of this lesion remains uncertain. Design and MethodsThe clinical and pathological characteristics, including SOX11 expression, of 23 cases initially diagnosed as in situ mantle cell lymphoma were studied. ResultsSeventeen of the 23 cases fulfilled the criteria for in situ mantle cell lymphoma. In most cases, the lesions were incidental findings in reactive lymph nodes. The t(11;14) was detected in all eight cases examined. SOX11 was positive in seven of 16 cases (44%). Five cases were associated with other small B-cell lymphomas. In two cases, both SOX11-positive, the in situ mantle cell lymphoma lesions were discovered after the diagnosis of overt lymphoma; one 4 years earlier, and one 3 years later. Twelve of the remaining 15 patients had a follow-up of at least 1 year (median 2 years; range, 1-19.5), of whom 11 showed no evidence of progression, including seven who were not treated. Only one of 12 patients with an in situ mantle cell lymphoma lesion and no diagnosis of mantle cell lymphoma at the time developed an overt lymphoma, 4 years later; this case was also SOX11-positive. The six remaining cases were diagnosed as mantle cell lymphoma with a mantle zone pattern. Five were SOX11-positive and four of them were associated with lymphoma without a mantle zone pattern. ConclusionsIn situ mantle cell lymphoma lesions are usually an incidental finding with a very indolent behavior. These cases must be distinguished from mantle cell lymphoma with a mantle zone pattern and overt mantle cell lymphoma because they may not require therapeutic intervention.Key words: in situ mantle cell lymphoma, in situ involvement by mantle cell-lymphoma-like cells, indolent behavior. Citation: Carvajal-Cuenca

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Histologic transformation of low-grade B-cell lymphoma to diffuse large B-cell lymphoma is associated with poor prognosis. Although plasma cell differentiation is common in these lymphomas, an overt plasmablastic transformation (PBL-T) has been only rarely reported. We report 6 cases of PBL-T occurring in 3 chronic lymphocytic leukemias (CLL) and 3 follicular lymphomas. Five patients were men, and the mean age was 65 years (range, 52 to 72 y). None of them had history of immunodeficiency. In 3 cases the PBL-T occurred 34 to 85 months after the initial diagnosis, and in 3 it was detected simultaneously with the small cell component at diagnosis. All patients received chemotherapy after transformation, and 4 died 4 to 24 months after this diagnosis. In 3 cases, PBL-T occurred in an extranodal site. All PBL-Ts had immunoblastic morphology with admixed plasma cells, were CD20 and PAX5 negative, expressed λ light chain, and 5 were CD138 positive. All cases were negative for HHV8, and only 1 PBL-T was Epstein-Barr virus positive. Evidence of a clonal relationship between the small cell and PBL-T components was found in 5 cases. In 2 CLL cases, both components had 13q deletions, and in all follicular lymphoma cases both components harbored the t(14;18) translocation. MYC translocations were observed in 2 cases transformed from a CLL. In conclusion, PBL-T expands the clinicopathologic spectrum of the transformation of low-grade B-cell lymphomas. These transformed tumors are clinically, histologically, and phenotypically similar to primary plasmablastic lymphomas, but they are not associated with immunodeficiency and rarely have Epstein-Barr virus infection or MYC alterations.