A Review of Circulating Tumor DNA as a Biomarker Guide for Total Neoadjuvant Therapy in Patients with Locally Advanced Rectal Cancer

PURPOSE

Non-operative management of patients with locally advanced rectal cancer (LARC) is emerging as a popular approach for patients that have no evidence of disease following neoadjuvant therapy. However, high rates of local recurrence or distant metastases have highlighted the urgent need for robust biomarker strategies to aid clinical management of these patients.

METHODS

This review summarizes recent advances in the utility of cell-free (cf) and circulating tumor (ct) DNA as potential biomarkers to help guide individualized non-operative management strategies for LARC patients receiving neoadjuvant therapy.

RESULTS

Liquid biopsies and the detection of cfDNA/ctDNA is an emerging technology with the potential to provide a non-invasive approach to monitor disease response and improve the identification of patients with LARC that would best benefit from non-operative management.

CONCLUSIONS

Substantial work is still needed before cfDNA/ctDNA monitoring can be widely adopted in the clinical setting. Studies reviewed herein highlight several areas of opportunity for improving the effectiveness and utility of cfDNA/ctDNA for managing patients with LARC.

Survey results of US radiation oncology providers' contextual engagement of watch-and-wait beliefs after a complete clinical response to chemoradiation in patients with local rectal cancer

Background

Watchful waiting in rectal cancer patients with a complete clinical response (cCR) to chemoradiation therapy (CRT) forgo upfront resection has been proposed. Growing evidence suggests that a watch-and-wait approach using resection for salvage of local recurrence may improve quality of life without jeopardizing outcomes. The current acceptance of watch-and-wait by US radiation oncologists (ROs) is unknown.

Methods

US ROs completed our IRB-approved anonymous e-survey regarding non-surgical management of patients who achieved a cCR to neoadjuvant CRT. Self-ranked knowledge of the OnCoRe Project-UK prospective observational study of watch-and-wait-was tested for its association with ROs' attitudes using the Chi-squared or Fisher's test, as indicated. Supporters of observation are self-identified.

Results

Of the 220 respondents, 48% (n=106) of respondents support watchful waiting and 48% claimed familiarity with the OnCoRe Project. Respondents supporting observation were more likely to be familiar with the publication (P=0.029). Among watch-and-wait supporters, 59% (n=62) felt comfortable discussing this approach and 41% preferred the conversation be initiated by other specialists. There was no association between comfort level in discussing watch-and-wait and familiarity with the OnCoRe Project. ROs treating more than 10 locally advanced rectal cancer (LARC) patients annually felt more comfortable discussing watch-and-wait (P=0.015) compared to ROs seeing fewer patients.

Conclusions

Almost half of surveyed US ROs support watch-and-wait, though many do not feel comfortable discussing this paradigm with patients. Knowledge of the OnCoRe Project is associated with support of watch-and-wait, yet not comfort level in leading the discussion. These results inform provider attitudes toward future clinical study participation.

The fine line between regional and metastatic pelvic lymph nodes in rectal cancer: Patterns of care among U.S. radiation oncologists

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Background: Management of rectal cancer with involved lateral pelvic lymph nodes (LPLNs) at the time of diagnosis – the stage we refer institutionally to as Stage 3.5 – is controversial. Asian investigators consider internal, external and common iliac lymph nodes (LNs) as regional disease and treat these patients (pts) with curative intent, which often includes LPLN dissection. Conversely, AJCC 7thedition classifies internal iliac LNs as regional, whereas both external and common iliac LNs as metastatic. NCCN guidelines recommend definitive trimodality therapy for Stage III rectal cancer, and palliative chemotherapy for Stage IV disease. Radiation oncologists (ROs) in the U.S. irradiate iliac LNs in the setting of other pelvic malignancies, but it is unknown how they approach newly diagnosed rectal cancer pts with LPLN involvement. Methods: We conducted an anonymous IRB-approved online survey of practicing U.S. ROs, probing their approach to management of rectal cancer pts with clinically involved LPLNs. Results: We received 220 responses. Among the responders, 85 are academically affiliated and the majority self-declared a specialization in treating GI malignancies, with 98 seeing more than 10 rectal cancer pts annually. Among respondents, 10.5% and 34.2% recommend biopsy of clinically involved internal and common iliac LNs, respectively. The vast majority of responders – 98.6% and 94.5% – treat involved internal and common iliac LNs with curative intent, respectively. Respondents recommend treatment intensification to involved internal iliac LNs by dissection of the nodal basin (88.2%) and radiation therapy (RT) boost (59.1%), and treatment intensification to involved common iliac LNs by LN dissection (76.4%) and RT boost (63.6%). Conclusions: Our analysis reveals that the vast majority of surveyed U.S. ROs approach pts with involved LPLNs, both regional (internal iliac) and metastatic (i.e. common iliac) with curative intent. They recommend treatment intensification with surgical resection and/or RT boost to involved nodes. Prospective clinical trials need to determine the appropriate management of pts with Stage 3.5 rectal cancer.

Utilization of imaging modalities in the staging of newly diagnosed rectal cancer: A survey of U.S. radiation oncologists

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Background: Accurate staging is crucial for management of patients (pts) with newly diagnosed rectal cancer. Endorectal ultrasound (EUS) has been a commonly used imaging modality for almost two decades, with magnetic resonance imaging (MRI) now preferred by national guidelines. Routine positron emission tomography (PET) is not recommended for initial staging. The current utilization of imaging modalities by radiation oncologists (ROs) in staging newly diagnosed rectal cancer pts in the United States is unknown. Methods: We conducted an anonymous IRB-approved online survey of practicing U.S. ROs. Respondent characteristics were tested for association with self-assessed utilization of imaging modalities using Chi-squared test. Staging 75% of more rectal cancer pts with a given modality was defined as high utilization. Results: We received 220 responses from practicing U.S. ROs. Among the responders, 85 are academically affiliated and the majority specialize in treating GI malignancies, with 98 seeing more than 10 rectal cancer pts annually. Most respondents utilize all three imaging modalities for rectal cancer staging - EUS, MRI and PET/CT. Fifty two percent and 38% of respondents are high utilizers of EUS and MRI, respectively. Nearly half (47%) of respondents are high PET utilizers. High utilization of PET was associated with practice in a private setting (p < 0.05) and being within 10 years from residency training completion (p < 0.05). Conclusions: Our analysis reveals a wide discordance between national guidelines and the practice patterns among U.S. ROs, with underutilization of MRI and overutilization of PET/CT. Substantial cost savings could be realized by following national guidelines recommendations to omit the routine use of PET/CT in the initial evaluation of pts with rectal cancer.