Detection of Molecular Residual Disease Using Personalized Circulating Tumor DNA Assay in Patients With Colorectal Cancer Undergoing Resection of Metastases

PURPOSE

More than 50% of patients with stage IV colorectal cancer (metastatic colorectal cancer [mCRC]) relapse postresection. The efficacy of postoperative systemic treatment is limited in this setting. Thus, these patients would greatly benefit from the use of a reliable prognostic biomarker, such as circulating tumor DNA (ctDNA) to identify minimal or molecular residual disease (MRD).

PATIENTS AND METHODS

We analyzed a cohort of 112 patients with mCRC who had undergone metastatic resection with curative intent as part of the PREDATOR clinical trial. The study evaluated the prognostic value of ctDNA, correlating MRD status postsurgery with clinical outcomes by using a personalized and tumor-informed ctDNA assay (bespoke multiple PCR, next-generation sequencing assay). Postresection, systemic therapy was given to 39.2% of the patients at the discretion of the treating physician.

RESULTS

Postsurgical, MRD positivity was observed in 54.4% (61 of 112) of patients, of which 96.7% (59 of 61) progressed at the time of data cutoff (hazard ratio [HR]: 5.8; 95% CI, 3.5 to 9.7; P < .001). MRD-positive status was also associated with an inferior overall survival: HR: 16.0; 95% CI, 3.9 to 68.0; P < .001. At the time of analyses, 96% (49 of 51) of patients were alive in the MRD-negative arm compared with 52.4% (32 of 61) in the MRD-positive arm. Patients who did not receive systemic therapy and were MRD-negative in the combined ctDNA analysis at two time points had an overall survival of 100%. In the multivariate analysis, ctDNA-based MRD status was the most significant prognostic factor associated with disease-free survival (HR: 5.78; 95% CI, 3.34 to 10.0; P < .001).

CONCLUSION

This study confirms that in mCRC undergoing resection of metastases, postoperative MRD analysis is a strong prognostic biomarker. It holds promises for being implemented in clinical decision making, informing clinical trial design, and further translational research.

Abstract 569: Correlation of variant allele frequency and mean tumor molecules with tumor burden in patients with solid tumors

Introduction: Two metrics are commonly used to quantify tumor-specific variants in cell-free DNA (cfDNA): the variant allele frequency (VAF), defined as the ratio of the number of variant alleles to wild-type alleles, and mean tumor molecules (MTM)/mL of plasma. The main difference between the two metrics is that molecular disease levels expressed in MTMs account for the total amount of cfDNA. Changes in cfDNA levels, which occur in response to cytotoxic therapies, surgery, and inflammation, have shown to impact the detection and quantification of tumor variants in plasma, leading to misinterpretation of the test results. Here we sought to explore the relationship between VAF and MTM and evaluate the performance of each metric in monitoring molecular residual disease.

Methods: We have analyzed 6569 plasma samples from 3389 patients including patients with primary diagnosis of colorectal cancer (n = 2413), breast (n = 170), pancreatic (n = 132), esophageal (n = 86), lung (n = 60), liver (n = 54), other cancers (n = 474) across multiple settings. ctDNA was quantified using a personalized and tumor-informed (bespoke mPCR NGS) assay. We examined the correlation between MTM and VAF for all ctDNA positive plasma samples (n = 1970) from 1283 patients using log-log regression. For patients with longitudinal plasma time points, further analyses on dynamic changes in MTM and VAF was performed to assess the sample-level discrepancy between the two metrics. Furthermore, the absolute values and the dynamic changes in MTM and VAF levels were plotted and compared against clinical truth based on imaging results and patient outcomes.

Results: Across all samples median cfDNA concentrations were 7.9 ng/mL (range: 1.3-381.6 ng/mL). Analysis of all ctDNA positive samples revealed a positive correlation between VAF and MTM, with R2 = 0.91 (slope: 0.86). From 3180 longitudinal plasma samples, we found 2.4% (76/3180) of samples, where changes relative to the previous time point were discordant between MTM and VAF. Interestingly, cfDNA concentrations in these samples were significantly altered. In general, cfDNA levels are representative of intrinsic cell turnover. While VAF is directly related to ctDNA, it is inversely related to cfDNA levels. Increased cfDNA levels were seen in the setting of active cytotoxic therapy, perioperatively, and in the setting of advanced disease, suggesting these settings may be prone for VAF to underestimate the true ctDNA burden. Here we provide evidence that failure of VAF to account for the dynamic changes in cfDNA concentration in plasma may result in misinterpretation of the patient's disease burden. This suggests that in certain indications MTM would be more clinically relevant than VAF.

Conclusion: Although both VAF and MTM are highly correlated, our analysis shows when cfDNA levels are significantly altered, MTM/mL provides a more accurate measure of molecular disease burden.

Citation Format: Antony Tin, Vasily Aushev, Ekaterina Kalashnikova, Raheleh Salari, Svetalana Shchegrova, Gordon Fehringer, Meenakshi Malhotra, Harini Ravi, Himanshu Sethi, Maxim Brevnov, Bernhard Zimmermann, Angel Rodriguez, Paul R. Billings, Alexey Aleshin. Correlation of variant allele frequency and mean tumor molecules with tumor burden in patients with solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 569.

Abstract 552: Circulating tumor DNA predicts disease recurrence in ovarian cancer patients

Introduction: Epithelial ovarian, fallopian tube, and peritoneal cancer (EOC) is the most lethal gynecologic malignancy with a 5-year survival rate of 47%. While primary treatment generally results in remission, most patients relapse within 3 years. CA-125 is a commonly used biomarker for recurrence detection, however, it lacks specificity and is not associated with improved survival. Here we examine the utility of circulating tumor DNA (ctDNA) as a biomarker for EOC by assessing its relationship to patient outcome and CA-125 when measured pre-surgically and during patient monitoring.

Methods: This study included patients diagnosed with stage I-IV EOC with plasma samples collected pre-surgically (n=44) and a group of patients (n=22) with serially collected samples after surgery. Median follow-up for patients with pre-surgical samples and with prospectively collected samples was 29 months (range: 6-150) and 15 months (range: 0.6-26), respectively. Whole exome sequencing was performed on patient tumors and matched normal tissue to design patient-specific ctDNA assays (bespoke mPCR NGS assay) for variant detection in plasma samples. The relationship between ctDNA status, CA-125 levels, and recurrence-free survival (RFS) were evaluated (Fisher's exact, log-rank test).

Results: Among patients with presurgical plasma samples high-grade serous was the most common histological subtype 66% (29/44). Endometrioid represented 11% (5/44) of tumors and 23% (10/44) were tumors of other epithelial subtypes. In this cohort 75% (33/44) had early-stage disease, 7% (3/44) were metastatic and 18% (8/44) had the unstaged disease. The presence of ctDNA was observed in 73% of samples at baseline with detection rates of 69% (20/29) for serous and 80% (4/5) for endometrioid histologies. Pre-surgical ctDNA detection was significantly associated with a higher grade (p=0.003). All patients with ctDNA negative status at baseline (n=12) survived until the end of follow-up (median: 25 months), while 3 deaths were observed among ctDNA positive patients (n=32; p=0.003).

In the sub-cohort of patients with prospective post-surgical plasma collection, ctDNA was observed in samples of all patients who relapsed (7/7; 100% sensitivity). ctDNA detection preceded radiological findings by a median of 9 months (range: 2-36). None of the patients with ctDNA negative status within 6 months after enrollment experienced disease progression (13/13; 100% specificity). The presence of ctDNA was observed to be a strong predictor of relapse (HR: 12.75, 95%CI: 1.7-94 p&lt;0.0001), while CA-125 was not significantly associated with RFS (HR: 1.3, 95%CI: 0.3-6.3; p=0.09).

Conclusions: The presence of ctDNA post-surgically is highly prognostic of decreased RFS and was found to be a stronger predictor of disease progression than CA-125 monitoring. These results suggest that monitoring ctDNA could be a useful tool in clinical decision making for patients with EOC.

Citation Format: Jocelyn S. Chapman, William E. Pierson, Karen Smith-McCune, Geovanni Pineda, Reena M. Vattakalam, Alexandra Ross, Meredith A. Mills, Carlos J. Suarez, Tracy Davis, Robert P. Edwards, Michelle Boisen, James M. Ford, June Y. Hou, Hsin-Ta Wu, Scott Dashner, Ekaterina Kalashnikova, Angel Rodriguez, Bernhard Zimmermann, Sarah Sawyer, Himanshu Sethi, Alexey Aleshin. Circulating tumor DNA predicts disease recurrence in ovarian cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 552.

Serial circulating tumor DNA analysis to assess recurrence risk, benefit of adjuvant therapy, growth rate and early relapse detection in stage III colorectal cancer patients

3540

Background: Challenges in the postoperative management of stage III colorectal cancer include: 1) selection of high-risk patients for adjuvant chemotherapy (ACT), 2) lack of markers to assess ACT efficacy, 3) assessment of recurrence risk after ACT, and 4) lack of markers to guide treatment decisions for high-risk patients e.g. additional therapy or intensified surveillance. Circulating tumor DNA (ctDNA) is a promising marker with potential to mitigate the challenges. Here we used serial ctDNA measurements to assess the correlation between recurrence and ctDNA detection: postoperative, during and after ACT, and during surveillance; and to assess growth rates of metachronous metastases. Uniquely, we also used concurrent CT scans and ctDNA measurements to compare the sensitivity for detecting recurrence. Methods: Stage III CRC patients treated with curative intent at Danish and Spanish hospitals in 2014-2019 were recruited (n = 166). Blood samples (n = 1227) were collected prior to and immediately after surgery, and every third month for up to 36 months. Per patient 16 personal mutations were used to quantify plasma ctDNA (Signatera, bespoke mPCR NGS assay). Results: Detection of ctDNA was a strong recurrence predictor, both postoperatively (HR 7.2, 95% CI 3.8-13.8, P< 0.001), directly after ACT (HR = 18.2, 95% CI 7.1-46, P < 0.001), and when measured serially after end of treatment (HR = 41, 95% CI 16-100, P < 0.001). The recurrence rate of postoperative ctDNA positive patients treated with ACT was 80% (16/20). Patients who stayed ctDNA positive during ACT all recurred. Serial post-treatment ctDNA measurements revealed exponential growth for all recurrence patients following either a SLOW (26%-increase/month) or a FAST (126%-increase/month) pattern (P < 0.001). From ctDNA detection to radiologic recurrence, ctDNA levels of FAST patients increased by a median 117-fold, and up to 554-fold. The 3-year overall survival was 43% for FAST patients and 100% for SLOW and non-recurrence patients (HR = 41.3, 95% CI 7.5-228, P < 0.001). Coinciding CT scans and ctDNA measurements (n = 113 patients, 235 coinciding events, median 2 per patient) showed a high agreement (92%) and ctDNA either detected residual disease before the CT scan (n = 7 patients) or at the same time (n = 14 patients). The median lead-time was 7.5 months. Conclusions: The study confirmed the prognostic power of serial postoperative ctDNA analysis. Moreover, it provided novel analyses demonstrating that ctDNA is more sensitive for recurrence detection than CT scans and can be used for tumor growth rate assessments. The difference between FAST and SLOW growing tumors suggest that growth rates could guide whom to start on systemic therapy rapidly and whom to send for diagnostic imaging. Altogether, the study highlights many potential utilities of ctDNA in guiding clinical decision-making.

Personalized, ctDNA analysis to detect minimal residual disease and identify patients at high risk of relapse with multiple myeloma

8029

Background: Despite treatment with high-dose chemotherapy followed by autologous stem cell transplantation (AHCT), MM patients invariably relapse. MRD-negativity post-AHCT has emerged as the most important prognostic marker. Currently, MRD in MM is monitored via bone marrow aspirate sampling. Marrow MRD assays are limited by the spatial heterogeneity of marrow MM localization; extramedullary disease and sampling variability of marrow aspiration. Sensitive, non-invasive blood-based MRD assay is an unmet need. ctDNA as a noninvasive biomarker can be utilized to predict relapse in MM. Here we attempt to evaluate MRD using ctDNA in AHCT recipients with MM. Methods: In this retrospective, single-center study, we analyzed ctDNA MRD in blood samples collected from 28 patients with MM after upfront AHCT. A total of 80 plasma timepoints were available pre and post AHCT with a median follow-up of 92.4 months. Multiparameter flow cytometry (MFC) at 10-4 level was used to assess the MRD from the BM biopsy. Individual bone marrow aspirates or FFPE slides from the time of MM diagnosis and matched normal blood were whole-exome sequenced, and somatic mutations were identified. MRD assessment at 3 months post-AHCT was performed by ctDNA analysis using a personalized, tumor-informed (SignateraTM, bespoke mPCR NGS assay). The prognostic value of ctDNA was evaluated by correlating MRD status with clinical outcomes. Results: Table provides the baseline disease characteristics. Median age was 67 [41-75] years and 16 [57.1%] were males. ctDNA was detectable in 70.8% (17/24) of pre-AHCT, 53.6% (15/28) of ̃3 months post-AHCT, and 39.2% (11/28) of patients during the surveillance phase post-AHCT. Of the 15 ctDNA MRD positive patients, 93.3% (n=14) experienced relapse on follow-up (hazard ratio: 5.64; 95% CI: 1.8-17; p=0.0003). Patients negative for ctDNA at 3 months post-AHCT had significantly superior progression-free survival (PFS) compared to positive (median PFS, 84 months vs. 31 months; p=0.003) The positive predictive value (PPV) for relapse among patients positive for ctDNA at 3 months post-AHCT was 93.3%, and significantly higher than marrow MFC of 68.4%. Conclusions: Our study shows the feasibility that a tumor-informed assay on archival blood samples is predictive of relapse post-AHCT. Future prospective studies with real-time marrow NGS and ctDNA samples are needed to define the role of ctDNA in MM and its prognostic significance.[Table: see text]

Abstract PD9-02: Personalized ctDNA as a predictive biomarker in high-risk early stage breast cancer (EBC) treated with neoadjuvant chemotherapy (NAC) with or without pembrolizumab (P)

Background: In the I-SPY 2 TRIAL, the addition of P to standard NAC resulted in more than doubling of the pathologic complete response (pCR) rates for both hormone receptor-positive (HR+)/HER2- and triple-negative (TN) early breast cancer (EBC) patients (pts) compared to NAC only (Nanda et al, JAMA Oncol, 2020). At 3 years, distant recurrence-free survival (DRFS) rates in pts with pCR following NAC+P was &gt;95%. We hypothesized that ctDNA can serve as a predictive biomarker of response and survival in pts treated with NAC.

Methods: A personalized ctDNA test (Signatera) was performed on 511 serial plasma samples from 138 pts with high-risk HR+/HER2- (n=77) or TN (n=61) stage II/III EBC. Pts received P with paclitaxel (Tx) followed by AC (P arm, n=42) or standard NAC only (n=96), an exploratory subset of pts evaluated for P efficacy. Plasma was collected; pretreatment (T0), 3 weeks after treatment initiation (T1), between Tx+/-P and AC regimens (T2), and prior to surgery (T3). ctDNA was deemed positive with a minimum of 2 of the pt specific tumor mutation fragments detected in cfDNA. Association of ctDNA with response and survival was analyzed using logistic and Cox regressions with pCR and DRFS as endpoints. Median follow-up was 2.8 years.

Results: Detection of ctDNA decreased over time (P arm: T0-81%, T1-50%, T2-19%, T3-3%) and NAC only: T0-82%, T1-65%, T2-26%, T3-10%).

ctDNA data at T0 and T1 was available for 96% (132/138) of pts in P arm or NAC only (Table). Among ctDNA+ patients at baseline, clearance at T1 was significantly associated with pCR (OR=1.92, ctDNA+/-; OR=0.27, ctDNA+/+; LR p&lt;0.001). This association remained significant after adjustment for HR status and treatment (LR p&lt;0.001) and P arm or NAC only (P: LR p=0.03; NAC: LR p=0.01).

ctDNA data at T0, T1, and T2 was available for 86% (118/138) pts. (Table). Among all ctDNA+ pts at baseline, dynamics through T2 was associated with pCR (OR=1.44, ctDNA+/-/-; OR=0.33, ctDNA+/+/-, OR=0.12, ctDNA+/+/+; LR p=0.0011). This association remained significant when adjusted for HR status and treatment (LR p&lt;0.001). Analysis within individual treatments showed significant association for NAC (LR p=0.040) and a non-significant trend in NAC+P (LR p=0.063), likely due to smaller sample size.

All pts who achieved pCR were ctDNA- at T3 (n=34). Among those who failed to achieve pCR (n=81), DRFS was significantly better in ctDNA- (n=72/81; 20 in P and 52 in NAC) versus ctDNA+ pts (n=9/81; 1 in P and 8 in NAC) (adjusted HR 0.13; 95% CI 0.05-0.37).

Conclusions: These exploratory results align with our previous findings that early clearance of ctDNA during NAC treatment was significantly associated with increased likelihood of achieving pCR. Additionally, we show that ctDNA clearance can be an early surrogate marker for therapy response assessment. Residual ctDNA after neoadjuvant treatment was a significant predictor of metastatic recurrence and death. Personalized monitoring of ctDNA during the course of NAC is feasible and provides information that can be combined with imaging and pathology, and may help to optimize decision making for de-escalation or escalation of therapy. Larger studies are ongoing.

ctDNA dynamics and pCRctDNA status at T0 and T1 (n=132)ctDNA status at T0, T1, and T2 (n=118)ctDNA-/-ctDNA+/-ctDNA+/+ctDNA-/-/-ctDNA+/-/-ctDNA+/+/-ctDNA+/+/+Total, n (%)24 (18)28 (21)80 (61)22 (19)24 (20)43 (36)27 (23)pCR, n (%)9 (38)15 (54)11 (14)9 (41)12 (50)8 (19)2 (7)No pCR, n (%)15 (63)13 (46)69 (86)13 (59)12 (50)35 (81)25 (93)

Citation Format: Mark Jesus M Magbanua, Denise Wolf, Derrick Renner, Svetlana Shchegrova, Lamorna Brown Swigart, Christina Yau, Gillian Hirst, Hsin-Ta Wu, Ekaterina Kalashnikova, Antony Tin, Amy Delson, Douglas Yee, Angela DeMichele, Raheleh Salari, Angel Rodriguez, Bernhard Zimmermann, Himanshu Sethi, Alexey Aleshin, Paul Billings, Laura Esserman, Minetta Liu, Rita Nanda, Laura van ‘t Veer, I-SPY 2 Investigators. Personalized ctDNA as a predictive biomarker in high-risk early stage breast cancer (EBC) treated with neoadjuvant chemotherapy (NAC) with or without pembrolizumab (P) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD9-02.

Circulating tumor DNA analysis for assessment of recurrence risk, benefit of adjuvant therapy, and early relapse detection after treatment in colorectal cancer patients

11

Background: Timely detection of recurrence, as well as identification of patients at high risk of recurrence after surgery and after completion of adjuvant therapy, are major challenges in the treatment of colorectal cancer (CRC). Postsurgical circulating tumor DNA (ctDNA) analysis is a promising tool for the identification of patients with minimal residual disease (MRD) and a high risk of recurrence. The objective of this prospective, multicenter study was to determine whether serial postsurgical ctDNA analysis could identify the patients at high risk of recurrence, provide an assessment of adjuvant therapy efficacy and detect relapse earlier than standard-of-care radiological imaging. Methods: The cohort comprises 265 stage I-III CRC patients, the to-date largest cohort assessed for ctDNA. All patients had the tumor resected and a subset of 62.6% (166 /265) was additionally treated with ACT. Plasma samples (n = 1503) were collected at various time points for a median follow-up of 28.4 months (range: 1.2-51.0 months). Individual tumors and matched germline DNA were whole-exome sequenced and somatic single nucleotide variants (SNVs) were identified. Personalized multiplex PCR assays were designed to track tumor-specific SNVs (Signatera, bespoke mPCR NGS assay) in each patient’s plasma sample. Results: Postoperative ctDNA status prior to ACT was assessed in 218 patients, of which 9.17% (20/218) were identified to be MRD-positive and 75% (15/20) eventually relapsed. The remaining 25% (5/20) of MRD-positive patients that did not relapse, received ACT. In contrast, only 13.6% (27/198) of MRD-negative cases relapsed (HR: 11: 95% CI: 5.7-20; p < 0.001). Longitudinal ctDNA-positive status, post-definitive therapy (n = 202) was associated with a HR of 36 (95% CI: 16-81; p < 0.001). For a subset of 155 patients postoperative CEA and ctDNA measurements were compared, wherein, ctDNA-positive status was found to be significantly associated with RFS (HR, 7.1; 95% CI, 3.4-15; P < 0.001) compared to CEA (HR, 1.2; 95% CI, 0.46-3.1; P = 0.73). Serial ctDNA analysis detected MRD up to a median of 8 months (0.56 - 21.6 months) ahead of radiologic relapse. Conclusion: Postoperative ctDNA positive status was associated with markedly reduced RFS compared to CEA. The study also shows that effective therapy can be curative in a portion of MRD-positive patients. In a longitudinal setting, ctDNA analysis predicted the risk of recurrence and is a more reliable biomarker for treatment response monitoring.

Minimal residual disease (MRD) detection with circulating tumor DNA (ctDNA) from personalized assays in stage II-III colorectal cancer patients in a U.K. multicenter prospective study (TRACC)

102

Background: Numerous studies have shown the clinical utility of ctDNA, a non-invasive biomarker to detect MRD and stratify CRC patients who are more likely to relapse. We present an analysis of MRD detection in CRC patients from a prospective multicentre UK study, who were monitored pre- and post-surgery before adjuvant chemotherapy (ACT). Methods: The study recruited patients diagnosed with stage II-III CRC (n=122), including a subset of rectal patients who underwent tri-modality treatment (TMT). All patients had their primary tumor resected and 56% (68/122) received ACT. Paired plasma samples (n=244) were collected before surgery/neaodjuvant chemoradiotherapy and after surgery; median follow-up for survival was 15.48 months (0.16 - 42.1 months). Individual tumors and matched germline DNA were whole-exome sequenced and somatic single nucleotide variants (SNVs) identified. Multiplex PCR assays were designed to track tumor-specific SNVs (Signatera, bespoke mPCR NGS assay) in plasma samples. The study evaluated ctDNA status and clinical outcomes including radiologic imaging. Cox regression was used to calculate recurrence-free survival (RFS) in patients stratified by post-op ctDNA status. Patients were also stratified into low and high-risk groups based on the clinicopathological features. Multivariate analysis was performed with covariates: ctDNA, age, gender, laterality, stage, number of lymph node resected, MSI & TMB. Results: Pre-treatment ctDNA was detected in 93.4% (100/107) of patients. Post-operative ctDNA status prior to ACT was assessed in 107 patients, of whom, 13% (14/107) were MRD-positive (MRDpos). Of the MRDpos patients 42.9% (6/14) eventually relapsed. In contrast, only 8.6% (8/93) of MRD-negative (MRDneg) cases relapsed (HR: 10; 95% CI: 3.3-30; p<0.001). MRD rates stratified by risk features in each of the stages with respective recurrence rates are shown in Table. In stage III patients (n=64), 45.4% (5/11) of the MRDpos patients relapsed, whilst only 17% (9/53) of the MRDneg cases relapsed (HR: 9; 95% CI:2.6-32; p<0.0001). In the multivariate analysis, ctDNA status was the most significant prognostic factor associated with RFS (HR: 28.8, 95% CI: 3.5-234.1; p<0.001). Conclusions: Postoperative ctDNA analysis with tumor informed assay enables detection of CRC patients at high-risk of recurrence. Early detection of MRD could guide ACT decisions in intervention trials and is currently underway in TRACC. Clinical trial information: NCT04050345. [Table: see text]

The effect of surgical trauma on circulating free DNA levels in cancer patients-implications for studies of circulating tumor DNA

Detection of circulating tumor DNA (ctDNA) post‐treatment is an emerging marker of residual disease. ctDNA constitutes only a minor fraction of the cell‐free DNA (cfDNA) circulating in cancer patients, complicating ctDNA detection. This is exacerbated by trauma‐induced cfDNA. To guide optimal blood sample timing, we investigated the duration and magnitude of surgical trauma‐induced cfDNA in patients with colorectal or bladder cancer. DNA levels were quantified in paired plasma samples collected before and up to 6 weeks after surgery from 436 patients with colorectal cancer and 47 patients with muscle‐invasive bladder cancer. To assess whether trauma‐induced cfDNA fragments are longer than ordinary cfDNA fragments, the concentration of short (< 1 kb) and long (> 1 kb) fragments was determined for 91 patients. Previously reported ctDNA data from 91 patients with colorectal cancer and 47 patients with bladder cancer were used to assess how trauma‐induced DNA affects ctDNA detection. The total cfDNA level increased postoperatively—both in patients with colorectal cancer (mean threefold) and bladder cancer (mean eightfold). The DNA levels were significantly increased up to 4 weeks after surgery in both patient cohorts (P = 0.0005 and P ≤ 0.0001). The concentration of short, but not long, cfDNA fragments increased postoperatively. Of 25 patients with radiological relapse, eight were ctDNA‐positive and 17 were ctDNA‐negative in the period with trauma‐induced DNA. Analysis of longitudinal samples revealed that five of the negative patients became positive shortly after the release of trauma‐induced cfDNA had ceased. In conclusion, surgery was associated with elevated cfDNA levels, persisting up to 4 weeks, which may have masked ctDNA in relapse patients. Trauma‐induced cfDNA was of similar size to ordinary cfDNA. To mitigate the impact of trauma‐induced cfDNA on ctDNA detection, it is recommended that a second blood sample collected after week 4 is analyzed for patients initially ctDNA negative.

Variation in training requirements within general surgery: comparison of 23 countries

Background

Many differences exist in postgraduate surgical training programmes worldwide. The aim of this study was to provide an overview of the training requirements in general surgery across 23 different countries.

Methods

A collaborator affiliated with each country collected data from the country's official training body website, where possible. The information collected included: management, teaching, academic and operative competencies, mandatory courses, years of postgraduate training (inclusive of intern years), working‐hours regulations, selection process into training and formal examination.

Results

Countries included were Australia, Belgium, Canada, Colombia, Denmark, Germany, Greece, Guatemala, India, Ireland, Italy, Kuwait, the Netherlands, New Zealand, Russia, Saudi Arabia, South Africa, South Korea, Sweden, Switzerland, UK, USA and Zambia. Frameworks for defining the outcomes of surgical training have been defined nationally in some countries, with some similarities to those in the UK and Ireland. However, some training programmes remain heterogeneous with regional variation, including those in many European countries. Some countries outline minimum operative case requirement (range 60–1600), mandatory courses, or operative, academic or management competencies. The length of postgraduate training ranges from 4 to 10 years. The maximum hours worked per week ranges from 38 to 88 h, but with no limit in some countries.

Conclusion

Countries have specific and often differing requirements of their medical profession. Equivalence in training is granted on political agreements, not healthcare need or competencies acquired during training.

Characterization of clonal hematopoiesis of indeterminate potential mutations from germline whole exome sequencing data

1525

Background: Clonal hematopoiesis of Indeterminate Potential (CHIP) is an age-related phenomenon where somatic mutations accumulate in cells of the blood or bone marrow. It is a source of biological noise that causes false-positives in ctDNA analysis and is present in up to 20% of individuals over the age of 70. The presence of CHIP has been linked to an increased risk of hematologic cancers and cardiovascular disease. The Signatera assay filters CHIP mutations through tumor tissue and germline sequencing thereby reducing false-positive results and focuses on tumor-specific mutations for each patient. Methods: Whole exome sequencing data (average depth ~250x) analyzed from patients’ buffy coat (n = 159) was used to characterize CHIP mutations. Variant calling was performed using Freebayes variant caller with allele frequency threshold between 1% and 10%. Following which variant annotation and selection was performed based on the top 54 genes that are most implicated in myeloid disorders. The selected variants were further screened based on the reported variants in the literature and/or the Catalog of Somatic Mutations in Cancer (COSMIC). Results: The analysis revealed an average of 0.14 (0-2) CHIP mutations per patient with an average variant allele frequency of 3.49% (1%-8.5%). The most common CHIP mutations were observed in DNMT3A, (n = 17), TET2 (n = 7) and TP53 (n = 7) genes. The percentage of patients with at least 1 mutation found in DNMT3A, TET2, and TP53 were 4.2%, 1.94%, and 1.38%, respectively. Other genes containing CHIP mutation included CEBPA, ETV6, HRAS, PDGFRA, NRAS, KMT2A, EZH2, GATA2, GNAS at a frequency below 1%. CHIP mutations were not observed in patients younger than 40 years, but they increased in frequency with every decade of life thereafter. The incidence of CHIP increased from 0.04 for the 40-50 yrs age group to 0.18 for individuals older than 60. Further analysis of associations between incidence of CHIP and cancer type, prior exposure to chemotherapy as well as longitudinal evolution of CHIP mutations during cytotoxic treatment are underway and will be presented. Conclusions: CHIP, a common finding in the elderly population is an important factor to consider in ctDNA analysis and most frequently involves DNMT3A, TET2, and TP53 genes. The frequency of CHIP can be impacted by a number of other factors such as cytotoxic chemo- or radiotherapy.

Circulating tumor DNA to detect minimal residual disease, response to adjuvant therapy, and identify patients at high risk of recurrence in patients with stage I-III CRC

4009

Background: The clinical utility of tracking circulating tumor DNA (ctDNA) as a non-invasive biomarker for detecting minimal residual disease (MRD) and stratifying patients based on their risk of developing relapse has been well established in colorectal cancer (CRC). This study evaluates the detection and longitudinal monitoring of ctDNA in CRC patients pre- and post-operatively, during and after adjuvant chemotherapy (ACT). Methods: The prospective, multicenter cohort study recruited patients (n = 193) diagnosed with resected stage I-III CRC. Plasma samples (n = 1052) were collected at various timepoints with a median follow up of 21.6 months (4.6-38.5 months). Individual tumors and matched germline DNA were whole-exome sequenced and somatic mutations identified. Multiplex PCR assays were designed to 16 tumor-specific single-nucleotide variants to track ctDNA in plasma samples. The study evaluated the relationship between ctDNA status and clinical outcomes including radiologic imaging. Cox regression was used to calculate recurrence-free survival (RFS) in patients stratified by ctDNA status postoperatively and post-ACT. Multivariable analysis was performed with all clinical variables. Best model was selected according to Akaike Information Criterion. Results: Pre-operatively ctDNA was detected in 90% (n = 166/185) of the patients. Post-operative ctDNA status prior to ACT was assessed in 152 patients, of which 9.2% (14/152) were identified to be MRD-positive and 78.5% (11/14) eventually relapsed. In contrast, 10.1% (14/138) of MRD-negative cases relapsed (HR: 16.53; 95% CI: 7.19-38.02; p < 0.001). Longitudinal ctDNA-positive status, post-ACT (n = 84) and post definitive therapy (n = 139) was associated with a 27.92 HR (95% CI: 9.16-85.11; p < 0.001) and a 47.52 HR (95% CI: 17.34-130.3.; p < 0.001), respectively. In the multivariable analysis, longitudinal ctDNA status was the only significant prognostic factor associated with RFS (HR: 53.19, 95% CI: 18.87-149.90; p < 0.001). Serial ctDNA analysis detected MRD up to a median of 9.08 months (0.56-16.5 months) ahead of radiologic relapse with a sensitivity of 79.1% and specificity of 99%. Conclusions: Postoperative ctDNA analyses detect patients with high-risk of recurrence, with near 100% specificity. Early detection of MRD and longitudinal monitoring of ctDNA could guide treatment decisions. Intervention trials to assess the clinical benefit of ctDNA use are underway.

Abstract P5-01-04: Personalized monitoring of circulating tumor DNA during neoadjuvant therapy in high-risk early stage breast cancer reflects response and risk of metastatic recurrence

Background: The detection of circulating tumor DNA (ctDNA) during neoadjuvant therapy (NAT) may serve as an early indicator of emerging resistance and disease progression. In this study, we analyzed ctDNA from high-risk early breast cancer patients who received NAT and definitive surgery in the I-SPY 2 TRIAL (NCT01042379). We hypothesized that ctDNA can serve as a biomarker of response and survival in this setting.

Methods: ctDNA analysis was performed on 291 plasma samples from 84 high-risk stage II and III breast cancer patients randomized either to an investigational agent MK-2206, an AKT inhibitor, in combination with paclitaxel followed by doxorubicin and cyclophosphamide (AC) (n=52)—or standard-of-care (paclitaxel followed by AC) (n=32). HER2+ patients also received trastuzumab. Serial plasma was collected at pretreatment (T0), at 3 weeks after initiation of paclitaxel treatment (T1), between paclitaxel and AC regimens (T2), and after NAT prior to surgery (T3).

A personalized ctDNA test was designed to detect a set of 16 patient-specific somatic variants, initially identified from whole exome sequencing of pretreatment tumor, then tested in plasma samples. Regions containing the somatic variants were amplified from cell-free DNA using specific polymerase chain reaction primers. Amplified products were subjected to ultra-deep sequencing (mean: 94,000x) to detect somatic variants. Association between ctDNA and clinicopathologic variables was assessed using Fisher’s exact test. Association of ctDNA with response and survival was analyzed using logistic and Cox regressions, respectively. The survival endpoint of the study was distant disease-free survival. The median follow-up was 4.8 years.

Results: At pretreatment (T0), 61 of the 84 (73%) patients had detectable ctDNA. Pretreatment (T0) ctDNA positivity and levels (mean mutant molecules per mL of plasma) were significantly associated with increased tumor burden (clinical T stage T3/T4), more aggressive tumor biology (higher Mammaprint scores) and subtype (HER2+ and Triple negative). CtDNA detection during NAT decreased over time (T0- 73%; T1- 35%; T2- 14%; T3- 9%).

Of the 84 patients, 23 (27%) achieved pCR and all were ctDNA-negative after NAT (T3), while all 6 patients who had detectable ctDNA at T3 did not achieve pCR. Patients who cleared ctDNA early at T1 (n=27, 48% pCR rate) had significantly increased probability of achieving a pathologic complete response (pCR) compared to those who remained ctDNA-positive (n=29, 17% pCR rate; Odds ratio=4.33, Likelihood ratio p=0.012).

Patients who were ctDNA-positive at T3 (n=6) had significantly increased risk of metastatic recurrence (HR 14.7; 95% CI 1.6-131.5) compared to those who achieved pCR and were ctDNA-negative (n=17). The risk of metastatic recurrence in patients who cleared ctDNA during NAT was not significantly different from those who were negative at T0 and remained negative by T3 (hazard ratio, HR: 2.1, 95% CI: 0.22-20.2). Interestingly, patients who were ctDNA-negative (n=37) but failed to achieve pCR had similar risk of metastatic recurrence with those who achieved pCR (HR 1.4; 95% CI 0.15-13.5).

Conclusions: Early clearance of ctDNA during NAT was significantly associated with increased likelihood of achieving pCR. Residual ctDNA after NAT was a significant predictor of metastatic recurrence, while clearance of ctDNA at any point during NAT was associated with improved outcomes. Taken together, personalized monitoring of ctDNA during NAT may aid in real-time assessment of treatment response and help fine-tune pCR as a surrogate endpoint of survival. Validation studies in a larger cohort are warranted.

Citation Format: Mark Jesus M Magbanua, Lamorna Brown-Swigart, Gillian Hirst, Christina Yau, Denise Wolf, Hsin-Ta Wu, Antony Tin, Svetlana Shchegrova, Himanshu Sethi, Raheleh Salari, Alexey Aleshin, Maggie Louie, Bernhard Zimmermann, Angela DeMichele, Minetta Liu, Amy Delson, Amy Jo Chien, Smita Asare, Laura Esserman, I-SPY 2 TRIAL Consortium, Laura van't Veer. Personalized monitoring of circulating tumor DNA during neoadjuvant therapy in high-risk early stage breast cancer reflects response and risk of metastatic recurrence [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-01-04.

Analysis of Plasma Cell-Free DNA by Ultradeep Sequencing in Patients With Stages I to III Colorectal Cancer

Importance

Novel sensitive methods for detection and monitoring of residual disease can improve postoperative risk stratification with implications for patient selection for adjuvant chemotherapy (ACT), ACT duration, intensity of radiologic surveillance, and, ultimately, outcome for patients with colorectal cancer (CRC).

Objective

To investigate the association of circulating tumor DNA (ctDNA) with recurrence using longitudinal data from ultradeep sequencing of plasma cell-free DNA in patients with CRC before and after surgery, during and after ACT, and during surveillance.

Design, Setting, and Participants

In this prospective, multicenter cohort study, ctDNA was quantified in the preoperative and postoperative settings of stages I to III CRC by personalized multiplex, polymerase chain reaction-based, next-generation sequencing. The study enrolled 130 patients at the surgical departments of Aarhus University Hospital, Randers Hospital, and Herning Hospital in Denmark from May 1, 2014, to January 31, 2017. Plasma samples (n = 829) were collected before surgery, postoperatively at day 30, and every third month for up to 3 years.

Main Outcomes and Measures

Outcomes were ctDNA measurement, clinical recurrence, and recurrence-free survival.

Results

A total of 130 patients with stages I to III CRC (mean [SD] age, 67.9 [10.1] years; 74 [56.9%] male) were enrolled in the study; 5 patients discontinued participation, leaving 125 patients for analysis. Preoperatively, ctDNA was detectable in 108 of 122 patients (88.5%). After definitive treatment, longitudinal ctDNA analysis identified 14 of 16 relapses (87.5%). At postoperative day 30, ctDNA-positive patients were 7 times more likely to relapse than ctDNA-negative patients (hazard ratio [HR], 7.2; 95% CI, 2.7-19.0; P < .001). Similarly, shortly after ACT ctDNA-positive patients were 17 times (HR, 17.5; 95% CI, 5.4-56.5; P < .001) more likely to relapse. All 7 patients who were ctDNA positive after ACT experienced relapse. Monitoring during and after ACT indicated that 3 of the 10 ctDNA-positive patients (30.0%) were cleared by ACT. During surveillance after definitive therapy, ctDNA-positive patients were more than 40 times more likely to experience disease recurrence than ctDNA-negative patients (HR, 43.5; 95% CI, 9.8-193.5 P < .001). In all multivariate analyses, ctDNA status was independently associated with relapse after adjusting for known clinicopathologic risk factors. Serial ctDNA analyses revealed disease recurrence up to 16.5 months ahead of standard-of-care radiologic imaging (mean, 8.7 months; range, 0.8-16.5 months). Actionable mutations were identified in 81.8% of the ctDNA-positive relapse samples.

Conclusions and Relevance

Circulating tumor DNA analysis can potentially change the postoperative management of CRC by enabling risk stratification, ACT monitoring, and early relapse detection.

Personalized Detection of Circulating Tumor DNA Antedates Breast Cancer Metastatic Recurrence

PURPOSE

Up to 30% of patients with breast cancer relapse after primary treatment. There are no sensitive and reliable tests to monitor these patients and detect distant metastases before overt recurrence. Here, we demonstrate the use of personalized circulating tumor DNA (ctDNA) profiling for detection of recurrence in breast cancer.

EXPERIMENTAL DESIGN

Forty-nine primary patients with breast cancer were recruited following surgery and adjuvant therapy. Plasma samples (n = 208) were collected every 6 months for up to 4 years. Personalized assays targeting 16 variants selected from primary tumor whole-exome data were tested in serial plasma for the presence of ctDNA by ultradeep sequencing (average >100,000X).

RESULTS

Plasma ctDNA was detected ahead of clinical or radiologic relapse in 16 of the 18 relapsed patients (sensitivity of 89%); metastatic relapse was predicted with a lead time of up to 2 years (median, 8.9 months; range, 0.5-24.0 months). None of the 31 nonrelapsing patients were ctDNA-positive at any time point across 156 plasma samples (specificity of 100%). Of the two relapsed patients who were not detected in the study, the first had only a local recurrence, whereas the second patient had bone recurrence and had completed chemotherapy just 13 days prior to blood sampling.

CONCLUSIONS

This study demonstrates that patient-specific ctDNA analysis can be a sensitive and specific approach for disease surveillance for patients with breast cancer. More importantly, earlier detection of up to 2 years provides a possible window for therapeutic intervention.

Bespoke circulating tumor DNA (ctDNA) analysis as a predictive biomarker in solid tumor patients (pts) treated with single-agent pembrolizumab (P)

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Background: Limited data exist in the clonal dynamics of serial ctDNA as a predictive biomarker in advanced solid tumor pts receiving immune checkpoint blockade. Methods: Pts with mixed solid tumors received single agent P (anti-PD-1) 200 mg IV Q3wks in the investigator-initiated phase II INSPIRE trial (NCT02644369). ctDNA was assayed at baseline (B) and start of cycle 3 (C3) using a pt-specific amplicon-based NGS assay (Signatera™). Samples were considered ctDNA positive if ≥2 of 16 pt-specific targets met the qualifying confidence score threshold. Results: Results of 70 pts are presented. Demographics: male 46%; median age=60 yrs (range 21–82); head and neck (20%), triple negative breast (14%) and ovarian (14%) cancers comprised the major malignancies. Median no. of P cycles=4 (range 2–35); follow up was 14m (range 2–29); RECIST responses: CR 2.9% (n=2), PR 17% (n=12), CBR (CR+PR+SD≥6 cycles) 31% (n=22), RECIST/clinical PD (n=43/10; 65%/15%). Median PFS=3.3m and median OS=17.8m. 68/70 pts had ctDNA detected at baseline (median=16/16 variants) demonstrating 97% sensitivity. Table shows correlation of ΔctDNA (ctDNAB compared to ctDNAC3) with clinical efficacy parameters, whereas ctDNAB values did not reach statistical significance. Conclusions: A strong correlation exists between ΔctDNA with OS, PFS, CBR and ORR with P, suggesting it is a potential predictive biomarker in pts with mixed solid tumors. Clinical trial information: NCT02644369. [Table: see text]