medwireNews: The circulating tumor cell (CTC) count can identify patients with limited-stage small-cell lung cancer (SCLC) who are likely to have poor survival outcomes despite treatment, report researchers who have identified 15 cells per 7.5 mL as the optimal cutoff.
They explain that previous studies have identified thresholds of two and 50 CTCs per blood draw as being prognostic, but note that “these analyses were performed in heterogeneous patient populations” including individuals with limited- and extensive-stage disease.
Therefore, Fiona Blackhall, from the Christie NHS Foundation Trust in Manchester, UK, and co-investigators drew on the phase III CONVERT trial that investigated once-daily versus twice-daily chemoradiotherapy with curative intent in a cohort of 547 limited-stage SCLC patients.
Of the 75 participants included in the current analysis, CTCs were detected in 60%; the median count was one per 7.5 mL blood sample and the range was 0–3750 cells.
Although the analysis validated the previously proposed cutoff values of two and 50 CTCs, the optimal threshold for classifying patients into favorable and unfavorable prognosis groups was found to be 15 CTCs.
Specifically, progression-free survival was significantly longer for the 58 participants with a CTC count below 15 than for the 17 with at least 15 CTCs, at a median of 19.0 and 5.5 months, respectively. The difference in median overall survival was likewise significant, with corresponding durations of 26.7 and 5.9 months.
For patients with a CTC count of 15 cells or more, “survival was limited to ≤1 year in 70% and ≤2 years in 100% of patients,” say Blackhall et al in the Annals of Oncology.
And they write: “The detection of ≥15 CTCs in [limited-stage]-SCLC provides useful prognostic insight to improve disease stratification beyond clinical factors alone with potential future therapeutic application in patient selection for maintenance therapy and rationalising treatment in patients with the highest probability of achieving a disease-free interval and cure with [concurrent chemoradiotherapy] alone.”
Speaking to medwireNews, Blackhall pointed out that although 15 CTCs was found to be optimal in this study, “[t]he threshold will vary according to the series studied, and consensus on the threshold, derived from a range of studies, will be required for clinical implementation.”
Additionally, “further prospective validation – for instance, in studies of maintenance therapy – is warranted to define how best to incorporate this biomarker into clinical treatment algorithms for patients with small-cell lung cancer,” she said.
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