| Summary: | Abstract Background The combination of immunotherapy and chemotherapy has demonstrated an enhancement in progression-free survival (PFS) for individuals with advanced and metastatic triple-negative breast cancer (TNBC) when compared to the use of chemotherapy alone. Nevertheless, the extent to which different subgroups of metastatic TNBC patients experience this benefit remains uncertain. Objectives Our objective was to conduct subgroup analyses to more precisely identify the factors influencing these outcomes. Materials and methods The PubMed database was searched until Dec 2023 for studies that compared PD-1 checkpoint inhibitors plus chemotherapy (ICT) with chemotherapy (CT) alone. The primary outcome of interest was progression-free survival (PFS). Review Manager (RevMan) version 5.4. was used for the data analysis. Results Four randomized controlled trials (RCTs) comprising 2468 advanced and metastatic TNBC were included in this systematic review and meta-analysis. PFS surge with combined therapy was observed in White (HR 0.80 [0.70, 0.91], p = 0.0007) and Asian ethnicities (HR 0.73 [0.58, 0.93], p = 0.01) but not in Blacks (HR 0.72 [0.42, 1.24], p = 0.24). Overall, patients with distant metastasis demonstrated to derive the PFS benefit from additional immunotherapy (HR 0.87 [0.77, 0.99], p = 0.03); however, metastasis to individual distant site was associated with failure to achieve any treatment difference (Bone: HR 0.79 [0.41, 1.52], p = 0.49; Lung: HR 0.85 [0.70, 1.04], p = 0.11; Liver: HR 0.80 [0.64, 1.01], p = 0.06). While number of metastases > 3 also showed to impact the PFS advantage (HR 0.89 [0.69, 1.16], p = 0.39). While patients, regardless of prior chemotherapy, experienced a notable enhancement in PFS with ICT (Overall: HR 0.79 [0.71, 0.88], p < 0.0001; Yes: HR 0.87 [0.76, 1.00], p = 0.05; No: HR 0.67 [0.56, 0.80], p < 0.00001), those previously exposed to chemotherapy exhibited a significantly smaller PFS advantage compared to those without prior chemotherapy, as evidenced by a significant subgroup difference (Test for subgroup difference: P = 0.02, I2 = 82.2%). Patients lacking PD-L1 expression also failed to achieve any additional benefit from immunotherapy (PD-L1-: HR 0.95 [0.81, 1.12]; p = 0.54; PD-L1+: HR 0.73 [0.64, 0.85], p < 0.0001). Age, ECOG status, and presentation with de novo metastasis/recurrent shown no impact on IT-associated PFS advantage. Conclusions Patient- and treatment- related factors such as ethnicity, distant metastases, number of metastases (> 3), previous exposure to chemotherapy and PD-L1 expression, seem to influence or restrict the advantage in progression-free survival associated with the addition of immunotherapy to chemotherapy, as opposed to chemotherapy alone, in patients with advanced and metastatic TNBC. Larger studies are warranted to validate these outcomes.
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