Purpose: To investigate the associations between baseline and posttreatment circulating tumor cell (CTC) gene expression and outcome of patients enrolled in four North Central Cancer Treatment Group metastatic breast cancer (MBC) trials in which specimens were shipped (at 4°C) from community-based sites to a reference laboratory (Mayo Clinic, Rochester, MN).
Experimental design: Blood was collected at treating sites from MBC patients before (baseline), during, and at the end of treatment with erlotinib + gemcitabine (N0234), sorafenib (N0336), irinotecan + cetuximab (N0436), or paclitaxel-poliglumex + capecitabine (N0437). CTCs from 10 mL of EDTA blood were enriched with CD45 depletion, 24 to 30 hours postblood collection. Reverse transcription/quantitative PCR was used to determine cytokeratin-19 (CK19) and mammaglobin (MGB1) mRNA levels in CTCs from up to 13 (N0234), 16 (N0336), 18 (N0436), and 39 (N0437) patients. The gene expressions were normalized to β(2)-microglobulin and calibrated to healthy blood using the 2(-ΔΔCq) algorithm; positivity was defined as 2 or more.
Results: CK19+mRNA cells were detected in 56% to 75% and MGB1+mRNA cells in 23% to 38% of 86 patients at baseline. CK19+mRNA cells were detected in 30% to 67% and MGB1+mRNA cells in 14% to 64% of 110 postbaseline serial samples. The presence of baseline CK19+mRNA cells (P = 0.01) but not MGB1+mRNA cells (P = 0.14) was significantly associated with shorter overall survival. A decrease in MGB1+mRNA levels (baseline-week 8) seemed to be associated with clinical response (P = 0.05).
Conclusions: CTC gene expression analysis conducted by a reference laboratory is feasible when blood is collected from treating sites and processed 24 to 30 hours postcollection. The presence of baseline CK19+mRNA CTCs was associated with poor prognosis; a decrease in MGB1+mRNA CTCs may help predict response to therapy of MBC patients.