A Circulating Tumor Cell Assay For Tracking Treatment Response In Glioma

Purpose/Objective(s)Monitoring radiation therapy (RT) response in glioma patients is at times difficult, with post-RT effects and tumor progression often sharing similar appearances on magnetic resonance imaging. Circulating tumor cell (CTC) analysis provides biologically meaningful information that could contribute to the serial monitoring of treatment response with minimal risk to patients. We have previously established the effectiveness of a telomerase-based CTC assay for glioma. We present herein interim results of a prospective trial in patients with high grade glioma utilizing serial CTC assays throughout the RT course and during follow-up.Materials/MethodsPatients receiving RT and temozolomide for WHO grade 3 or 4 glioma were enrolled in an IRB-approved study in which CTC analysis was performed at time points before, during, and after RT. The assay incorporates a vector probe based on the human telomerase (hTERT) promoter, which amplifies the expression of green fluorescent protein (GFP) in cancer cells but not normal cells. The assay therefore identifies cancer cells with specificity, and is not affected by changes in or the absence of glioma cell surface markers.ResultsThe assay effectiveness in patients was not impeded by MGMT promoter methylation status, EGFR amplification, EGFR VIII expression, or IDH mutation status of tumors. Ten patients have now been followed for over six months, with a median age of 61 and 80% with grade 4 glioma. For the entire cohort, the mean pre-RT CTC count was 57.1 CTCs/mL (range 0-253) and the mean post-RT count was 3.9 CTCs/mL (range 1-9), with the overall decrease in CTC levels trending toward significance (p = 0.17). Median pre- and post-RT counts were 19.3 and 2.0 CTCs/mL, respectively. The patient with the highest detected pre-RT CTC level (253 CTCs/mL) derived a good symptomatic and radiographic response to RT, with post-RT analysis showing 1.3 CTCs/mL. In contrast, the two patients with > 45% increase in CTC levels between pre-RT and RT developed rapidly progressive disease requiring re-resection within 6 months of initial resection; one died of disease progression, but the other’s CTC levels subsequently decreased from 67.1 to 9.4 CTCs/mL after re-resection of the tumor.ConclusionsThese results support that CTCs may be detected in patients with high-grade glioma and that trends in CTC levels may reflect the tumor response to RT or resection. CTC assays may thus usefully complement conventional follow-up and imaging for tracking treatment response. Further updated results and implications for standard practice will be discussed. Purpose/Objective(s)Monitoring radiation therapy (RT) response in glioma patients is at times difficult, with post-RT effects and tumor progression often sharing similar appearances on magnetic resonance imaging. Circulating tumor cell (CTC) analysis provides biologically meaningful information that could contribute to the serial monitoring of treatment response with minimal risk to patients. We have previously established the effectiveness of a telomerase-based CTC assay for glioma. We present herein interim results of a prospective trial in patients with high grade glioma utilizing serial CTC assays throughout the RT course and during follow-up. Monitoring radiation therapy (RT) response in glioma patients is at times difficult, with post-RT effects and tumor progression often sharing similar appearances on magnetic resonance imaging. Circulating tumor cell (CTC) analysis provides biologically meaningful information that could contribute to the serial monitoring of treatment response with minimal risk to patients. We have previously established the effectiveness of a telomerase-based CTC assay for glioma. We present herein interim results of a prospective trial in patients with high grade glioma utilizing serial CTC assays throughout the RT course and during follow-up. Materials/MethodsPatients receiving RT and temozolomide for WHO grade 3 or 4 glioma were enrolled in an IRB-approved study in which CTC analysis was performed at time points before, during, and after RT. The assay incorporates a vector probe based on the human telomerase (hTERT) promoter, which amplifies the expression of green fluorescent protein (GFP) in cancer cells but not normal cells. The assay therefore identifies cancer cells with specificity, and is not affected by changes in or the absence of glioma cell surface markers. Patients receiving RT and temozolomide for WHO grade 3 or 4 glioma were enrolled in an IRB-approved study in which CTC analysis was performed at time points before, during, and after RT. The assay incorporates a vector probe based on the human telomerase (hTERT) promoter, which amplifies the expression of green fluorescent protein (GFP) in cancer cells but not normal cells. The assay therefore identifies cancer cells with specificity, and is not affected by changes in or the absence of glioma cell surface markers. ResultsThe assay effectiveness in patients was not impeded by MGMT promoter methylation status, EGFR amplification, EGFR VIII expression, or IDH mutation status of tumors. Ten patients have now been followed for over six months, with a median age of 61 and 80% with grade 4 glioma. For the entire cohort, the mean pre-RT CTC count was 57.1 CTCs/mL (range 0-253) and the mean post-RT count was 3.9 CTCs/mL (range 1-9), with the overall decrease in CTC levels trending toward significance (p = 0.17). Median pre- and post-RT counts were 19.3 and 2.0 CTCs/mL, respectively. The patient with the highest detected pre-RT CTC level (253 CTCs/mL) derived a good symptomatic and radiographic response to RT, with post-RT analysis showing 1.3 CTCs/mL. In contrast, the two patients with > 45% increase in CTC levels between pre-RT and RT developed rapidly progressive disease requiring re-resection within 6 months of initial resection; one died of disease progression, but the other’s CTC levels subsequently decreased from 67.1 to 9.4 CTCs/mL after re-resection of the tumor. The assay effectiveness in patients was not impeded by MGMT promoter methylation status, EGFR amplification, EGFR VIII expression, or IDH mutation status of tumors. Ten patients have now been followed for over six months, with a median age of 61 and 80% with grade 4 glioma. For the entire cohort, the mean pre-RT CTC count was 57.1 CTCs/mL (range 0-253) and the mean post-RT count was 3.9 CTCs/mL (range 1-9), with the overall decrease in CTC levels trending toward significance (p = 0.17). Median pre- and post-RT counts were 19.3 and 2.0 CTCs/mL, respectively. The patient with the highest detected pre-RT CTC level (253 CTCs/mL) derived a good symptomatic and radiographic response to RT, with post-RT analysis showing 1.3 CTCs/mL. In contrast, the two patients with > 45% increase in CTC levels between pre-RT and RT developed rapidly progressive disease requiring re-resection within 6 months of initial resection; one died of disease progression, but the other’s CTC levels subsequently decreased from 67.1 to 9.4 CTCs/mL after re-resection of the tumor. ConclusionsThese results support that CTCs may be detected in patients with high-grade glioma and that trends in CTC levels may reflect the tumor response to RT or resection. CTC assays may thus usefully complement conventional follow-up and imaging for tracking treatment response. Further updated results and implications for standard practice will be discussed. These results support that CTCs may be detected in patients with high-grade glioma and that trends in CTC levels may reflect the tumor response to RT or resection. CTC assays may thus usefully complement conventional follow-up and imaging for tracking treatment response. Further updated results and implications for standard practice will be discussed.