Tumor-infiltrating lymphocytes (TILs) represent a surrogate biomarker of anti-tumor, lymphocyte-mediated immunity. In early, triple-negative breast cancer, TILs have level 1B of evidence to predict clinical outcomes. TILs represent a promising biomarker to select patients who can experience a better prognosis with de-intensified cancer treatments and derive larger benefits from immune checkpoint inhibitors. However, the assessment and the validation of TILs as a biomarker require a prospective and rigorous demonstration of its clinical validity and utility, provided reproducible analytical performance. With pending data about the prospective validation of TILs' clinical validity to modulate treatments in early breast cancer, this review summarizes the most important current issues and future challenges related to the implementation of TILs assessments across all breast cancer subtypes and their potential integration into clinical practice.

BackgroundFollowing the introduction of immunotherapy (IO) in the first-line (1L) treatment in patients with non-small cell lung cancer (NSCLC) without sensitizing EGFR/ALK mutations, increasing real-world data depict how difficult it is to replicate data from clinical trials to clinical practice, with high rates of early treatment failure. In the context of chemo-IO, our study aims to compare platinum-pemetrexed-pembrolizumab combination to platinum-doublet alone in patients with low PD-L1 (<50%).MethodsWe retrospectively collected medical records from patients with stage IV non-squamous NSCLC with PD-L1<50%, consecutively treated at our Centre from 2016 to 2021. Patients were grouped according to 1L treatment received: chemo-IO (group A) or platinum-doublet (group B). Survival outcomes were analyzed and compared among the two groups.ResultsOverall, 105 patients were included: 49 in group A and 56 in group B. At data cut-off, median follow-up was 12.4 and 34.8 months, with 32/49 and 52/56 events for progression-free survival (PFS) and 21/49 and 29/56 events for overall survival (OS), respectively. No difference in PFS was observed between group B and group A (6.6 versus 8 months, HR 1.12, 95%CI 0.57-1.40). Patients receiving 1L platinum-doublet had significantly longer OS compared to those receiving chemo-IO (median OS 23.8 vs 14.9 months, HR 0.47, 95% CI 1.15- 3.98, p=0.01). 12 month-OS was 58% (95% CI 44-76%) in group A and 78% (95% CI 68-91%) in group B (p=0.040). Subgroup analysis identified KRAS G12C mutation as potentially affecting PFS in patients receiving chemo-IO (HR 0.29, 95% CI 0-10-0.91). The OS benefit of platinum-doublet was consistent across subgroups, with particular benefit in female sex, liver or pleural metastases, PD-L1 negative. Overall, only 46.9% of patients with progression received subsequent treatment in group A (15/32), compared to 86.5% in group B (45/52, all receiving 2L IO), with no difference in PFS to 2L (group A 3.7months, group B 4.1months, p=0.3).ConclusionsDespite small study population and differential follow-up, our study demonstrates that sequential use of 1L platinum-doublet and 2L IO is not inferior to 1L chemo-IO in non-squamous NSCLC with PD-L1<50%. In addition, we identified subgroups who might benefit differentially from the two approaches.

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