Elevated circulating tumor cell (CTC) blood levels (≥5 cells/7.5ml) convey a negative prognosis in metastatic castration-resistant prostate cancer but their prognostic significance in patients receiving chemotherapy is uncertain. The association between CTC counts (at baseline or after treatment), overall survival (OS), and response to docetaxel with lenalidomide was evaluated in a 208-patient subset from the MAINSAIL trial, which compared docetaxel-prednisone-lenalidomide and docetaxel-prednisone-placebo in metastatic castration-resistant prostate cancer patients. Baseline CTCs were <5 cells/7.5ml blood in 87 (42%) patients and ≥5 cells/7.5ml in 121 (58%) patients. Neither tumor response nor prostate-specific antigen response correlated with baseline CTCs. However, CTC count ≥5 cells/7.5ml was significantly associated with lower OS (hazard ratio: 3.23, p = 0.0028). Increases in CTCs from <5 cells/7.5ml to ≥5 cells/7.5ml after three cycles were associated with significantly shorter OS (hazard ratio: 5.24, p=0.025), whereas CTC reductions from ≥5 cells/7.5ml to <5 cells/7.5ml were associated with the best prognosis (p=0.003).
Patient summary: Our study in metastatic castration-resistant prostate cancer patients treated with docetaxel chemotherapy, with or without lenalidomide, showed that patient survival was best predicted by circulating tumor cell count at the start of treatment. A rising circulating tumor cell count after three cycles of therapy predicted poor survival, while a decline predicted good survival.
Keywords: Circulating tumor cells; Docetaxel; Lenalidomide; Metastatic castration-resistant prostate cancer; Prostate cancer.
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