A pilot study of clinical evidence for phenotypic circulating tumor cell counts in stage II/III rectal cancer patients treated with neoadjuvant chemoradiotherapy

OBJECTIVE: To explore the clinical evidence of phenotypic circulating tumor cell (CTC) counts in stage II/III rectal cancer patients undergoing neoadjuvant chemoradiotherapy (nCRT). METHODS: We isolated CTCs from 5 mL of peripheral blood from each of 40 rectal cancer patients in stage II/III using a physical marker-based (size- and deformability-based) isolation method, thus enabling simultaneous capture and count of phenotypically diverse CTCs, including epithelial (E-), hybrid (H-), and mesenchymal (M-) CTCs, at initial diagnosis (pre-nCRT) and after nCRT (post-nCRT), prior to surgery. We examined the association between the phenotypic CTC counts and the key clinical outcomes, including tumor regression grade (TRG), postoperative pathological stage (ypStage), and recurrence/metastasis. RESULTS: Pre-nCRT M-CTC counts were significantly higher in patients with unfavorable ypStage II-III compared with those with ypStage 0-I (Mann-Whitney U test p = 0.044). In survival analyses, the presence of post-nCRT E-CTCs was significantly associated with reduced recurrence/metastasis-free survival (log-rank p = 0.023). CONCLUSIONS: This pilot study suggests that specific phenotypic CTC subtypes may be associated with postoperative pathological stage and recurrence/metastasis risk in rectal cancer patients treated with nCRT. Phenotype-specific CTC profiling may provide complementary, non-invasive information beyond conventional pathological indicators; however, further validation in larger, independent cohorts is required.