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. Author manuscript; available in PMC: 2014 Apr 14.
Published in final edited form as: Cancer J. 2011 Nov-Dec;17(6):438–450. doi: 10.1097/PPO.0b013e31823e69ac

TABLE 1.

Level-of-Evidence Scale and Group the Current CTC Tests

Phase I: New CTC test is developed (and refined) in a laboratory, specificity and sensitivity shown, first clinical data on cancer patients, first publication(s).
Phase II: New CTC test compared with existing CTC test (criterion standard, e.g., CellSearch) and “superior” findings demonstrated with regard to clinical relevance in a limited study.
Phase III: New CTC test is disseminated to other CTC-specialized laboratories, and results of the initial studies are reproduced (e.g., specificity, sensitivity, reproducibility in blinded ring experiments).
Phase IV: New CTC test is implemented in large-scale clinical trial(s) with defined endpoints (e.g., progression-free or overall survival) side-by-side with most established CTC test for the particular cohort of patients and stage and treatment. Circulating tumor cell testing in specialized laboratories.