Maria Pouyiourou

Abstract Cancer of unknown primary has a dismal prognosis, especially following failure of platinum-based chemotherapy. 10-20% of patients have a high tumor mutational burden (TMB), which predicts response to immunotherapy in many cancer types. In this prospective, non-randomized, open-label, multicenter Phase II trial (EudraCT 2018-004562-33; NCT04131621), patients relapsed or refractory after platinum-based chemotherapy received nivolumab and ipilimumab following TMB high vs. TMB low stratification. Progression-free survival (PFS) represented the primary endpoint; overall survival (OS), response rates, duration of clinical benefit and safety were the secondary endpoints. The trial was prematurely terminated in March 2021 before reaching the preplanned sample size ( n = 194). Among 31 evaluable patients, 16% had a high TMB ( > 12 mutations/Mb). Overall response rate was 16% (95% CI 6-34%), with 7.7% (95% CI 1-25%) vs. 60% (95% CI 15-95%) in TMB low and TMB high , respectively. Although the primary endpoint was not met, high TMB was associated with better median PFS (18.3 vs. 2.4 months) and OS (18.3 vs. 3.6 months). Severe immune-related adverse events were reported in 29% of cases. Assessing on-treatment dynamics of circulating tumor DNA using combined targeted hotspot mutation and shallow whole genome sequencing as part of a predefined exploratory analysis identified patients benefiting from immunotherapy irrespective of initial radiologic response.

INTRODUCTION: Chromosomal aberrations are known to drive metastatic spread, but their profile is still elusive in carcinoma of unknown primary (CUP). Therefore, the aim of this study was to characterize the chromosomal aberration pattern in CUP depending on histological and clinical features and to assess its prognostic impact together with chromothripsis, tumor mutational burden (TMB), microsatellite instability (MSI), and mutational profiles as potential prognostic biomarkers. METHODS: Chromosomal aberrations and chromothripsis were detected by methylation-based copy number variation (CNV) analysis, whereas TMB and MSI were calculated based on large next-generation sequencing (NGS) panels. Putative primaries were assigned by consensus between two independent oncologists. RESULTS: CNV losses varied depending on putative primaries and were more abundant in patients harboring TP53 mutations and/or deletions 17p. CNV loss was prognostically adverse in localized CUP treated with surgery and/or radiotherapy, but not in disseminated poor-risk CUP treated with palliative chemotherapy. CNV loss also worsened the prognosis in squamous cell CUP. Chromothripsis was detected in 18/59 (30.5%) patients without prognostic effect. TMB was highest in cases with MSI, squamous cell histology, and with lung, anal or cervical putative primaries. CONCLUSION: Overall, CNV, chromothripsis, TMB, and MSI profiles in CUP are reminiscent of biological characteristics known from other cancer entities without a unifying CUP-specific signature. Markedly, high-level CNV loss is an adverse predictive biomarker in localized but not disseminated chemotherapy-treated CUP. This implies that chromosomal losses drive CUP progression, but also increase susceptibility to chemotherapy, with both effects apparently leveling out in disseminated CUP.

BACKGROUND: Cancer of unknown primary (CUP) is defined as a primary metastatic malignancy, in which the primary tumor remains elusive in spite of a comprehensive diagnostic workup. The frequency and prognostic value of circulating tumor cells (CTCs), which are considered to be the source of metastasis, has not yet been systematically evaluated in CUP. METHODS: A total of 110 patients with a confirmed diagnosis of CUP according to the European Society for Medical Oncology (ESMO) guidelines, who presented to our clinic between July 2021 and May 2023, provided blood samples for CTC quantification using CellSearch methodology. CTC counts were correlated with demographic, clinical, and molecular data generated by comprehensive genomic profiling of tumor tissue. RESULTS: CTCs were detected in 26% of all patients at initial presentation to our department. The highest CTC frequency was observed among patients with unfavorable CUP (35.5%), while patients with single-site/oligometastatic CUP harbored the lowest CTC frequency (11.4%). No statistically significant association between CTC positivity and the number of affected organs (P = 0.478) or disease burden (P = 0.120) was found. High CTC levels (≥5 CTCs/7.5 mL; 12/95 analyzed patients) predicted for adverse overall survival compared to negative or low CTC counts (6-months overall survival rate 90% vs 32%, log-rank P < 0.001; HR 5.43; 95% CI 2.23-13.2). CTC dynamics were also prognostic for overall survival by landmark analysis (log-rank P < 0.001, HR 10.2, 95% CI 1.95-52.9). CONCLUSIONS: CTC frequency is a strong, independent predictor of survival in patients with CUP. CTC quantification provides a useful prognostic tool in the management of these patients.