Non-personalized monitoring of pre-operative therapy for rectal cancer - 11th International Symposium on Circulating Nucleic Acids in Plasma and Serum (CNAPS)

Anatoli Kustanovich ¹ Eli Sapir ² Ruth Schwartz ¹ Emilia Sloutsky ¹ Héloïse Benech ¹ Myriam Maoz ¹ Ayala Hubert ¹ Daniel Neiman ³ Asael Lubotzky ³ Sheina Piyanzin ³ Amit Arad ¹ Ruth Shemer ³ Yuval Dor ³ Albert Grinshpun ¹

¹Sharett Institute of Oncology, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
²Radiation Oncology Center, Assuta Ashdod University Hospital, Ashdod, Israel
³Department of Developmental Biology and Cancer Research, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel

Introduction: Locally advanced rectal cancer is a common malignancy which requires multimodal therapy, mainly pre-operative chemo-radiation (CRT). Currently, all patients undergo extensive surgery following CRT, frequently resulting in sphincter damage and morbidity. However, there is a potential population of 15-20% of patients who may not require surgery due to maximal response to CRT and no remaining tumor at surgery (named pathological-complete-response, pCR).

Here, we aim to monitor treatment efficacy and predict pCR by a liquid biopsy approach; detect colorectal-derived circulating cell-free DNA (CcfDNA) in plasma using tissue-specific methylation markers.

Methods: Consecutive patients referred to pre-operative CRT were enrolled. All patients gave informed consent and were treated with standard CRT protocol (5-6 weeks). Plasma was collected at baseline, at first and last day of each radiation week. cfDNA from plasma was bisulfite treated and sequencing libraries were prepared by amplification of colorectal-specific markers. Sequencing was performed using NextSeq 500 (Illumina).

Results: Twenty patients who completed CRT successfully and underwent surgery were enrolled. As expected, 20% of patients (4/20) had a maximal response defined as pCR or near-pCR. Yet, there was no significant difference in levels of CcfDNA at baseline between these groups. Interestingly, during the first month of treatment, weekly fluctuations in the level of total cfDNA and CcfDNA were observed, probably related to accumulating toxicity of CRT to a tumor and surrounding tissue.

Analyzing CcfDNA levels after receiving 18-22 Gy of treatment (second and third weeks) allows differentiating between pCR and non-pCR patients. Level of CcfDNA in pCR achievers was significantly lower; median of 17.6 vs. 28.4 in the non-pCR group (p=0.006). In addition, we also observed a significant decrease in CcfDNA levels in pCR-achieving patients (p=0.044) during the last (5-7) weeks of treatment.

Conclusions: Liquid biopsy using colorectal–specific methylation markers is feasible and enables to monitor treatment efficacy in rectal cancer patients.