Total neoadjuvant therapy (TNT) is currently the standard treatment for locally/locally advanced rectal cancer due to better response and fewer distant metastases. In TNT, sequential chemotherapy (CT) and chemoradiotherapy (CRT) are planned and depending on the treatment response, either surgery is performed or a watch and wait approach is applied. Depending on tumor localization and patient performance status, CT is planned as induction or consolidation. Most of the time, mFOLFOX6 and CAPOX are preferred as CT regimen. In proximal rectal cancer, surgery can be performed without CRT and only after CT. In locally/locally advanced rectal cancer, the aim is to avoid surgery as much as possible or to perform sphincter-sparing surgery if possible. Colonoscopy and pelvic MR at the time of diagnosis are the most important steps in staging, treatment selection and decision making. These two diagnostic methods should be repeated especially for watch and wait decision and for response evaluation after TNT.

ADAR 1 (Adenosine deaminase acting on RNA1) is an RNA editing enzyme that catalyzes the deamination of adenosine to inosine (A-to-I), a dynamic modification that can lead to a diverse transcriptome in a combinatorial manner. A defect in ADAR1-mediated RNA modification results in abnormal regulation of substrates that can affect phenotypic changes in cancer. This phenomenon of over-regulation is seen in many cancers such as colon, liver, lung, breast and esophageal cancers and in many cases promotes tumor progression. In studies, increased ADAR1 expression has been associated with lower survival and worse prognosis, especially in metastatic colon and gastric cancer. ADAR1 is also predicted to increase proliferation through both the AKT pathway and the mTOR pathway and therefore may be targeted in the near future.

ADAR1 expression is monitored by RNA-based real time PCR. In order to demonstrate increased expression, biopsies should be taken from the malignant tissue and the intact tissue of the patient and the biopsy should be stored under -80 C conditions immediately after biopsy to prevent RNA degradation. The tissue will not come into contact with nitrogen or formaldehyde.

In this study, sufficient biopsies from cancerous and intact tissue will be taken from patients with suspected rectal cancer, confirmed by pelvic MRI and consent for participation in the study, and fresh tissue will be stored at -80 C in the genetics laboratory. After the TNT plan is made by the investigators and the treatment is completed, both pelvic MRI and control rectoscopy will be performed for preoperative evaluation. Again, biopsies will be taken from diseased and healthy tissue and ADAR1 expression will be evaluated. The study is planned to include 50 participants and a period of one year is foreseen for tissue procurement/storage.

The investigators' aim in this study will be to determine whether ADAR1 expression level changes after TNT, whether this predicts clinical and pathological response, whether responses change according to the selected CT, whether there is a difference between CT induction-consolidation/RT short or long course, and the relationship between tumor DNA mismatch repair enzyme status and ADAR1 level. The investigators primary endpoint will be the effect of the change in ADAR1 expression level on the response after TNT (ORR). Secondary endpoints will be quality of life, recurrence-free survival (RFS) and overall survival (OS).

Colorectal cancer is the third most common cancer in both sexes, but it ranks second in mortality after lung cancer, with one in ten cancer deaths attributed to colorectal cancer. Total neoadjuvant therapy (TNT) is currently considered the standard of care for the treatment of locally advanced rectal cancer. In this approach, all non-surgical interventions, including multi-agent chemotherapy and concurrent chemoradiotherapy (CRT), are administered prior to surgical resection or the decision to opt for non-operative treatment. Accumulating evidence suggests that TNT improves survival in patients with locally advanced rectal cancer and is expected to reduce distant metastasis through systemic chemotherapy, thereby preventing the onset of micrometastases. TNT has also been associated with improved compliance, reduced toxicity, decreased need for and duration of ileostomy, and improved anal sphincter preservation rates following a watch-and-wait strategy, along with increased complete clinical response. Studies have shown that the rate of pCR in patients receiving TNT therapy is approximately 20-40%. Although numerous randomized controlled trials have evaluated different TNT strategies compared to standard KRT treatment in terms of KRT sequencing, systematic chemotherapy, radiotherapy modality, and TNT intensity, it is known that the TNT approach demonstrates superior survival benefit compared to adjuvant chemotherapy following neoadjuvant KRT. However, TNT theoretically offers several surgical advantages, including an increased likelihood of sphincter-preserving surgery and a reduced need for ileostomy; however, results across studies are inconsistent.

ADAR 1 (Adenosine deaminase acting on RNA1) catalyzes the C6 deamination of adenosine (A) to produce inosine (I) in RNA regions characterized by a double-stranded structure, a process known as adenosine deamination acting on RNA (ATIRE). This process is crucial for altering RNA structures and sequences in both coding and non-coding RNAs, influencing tumor characteristics, tumor stage, drug responses, and patient survival, thereby significantly contributing to cancer progression. The role of ADAR1 in promoting tumorigenesis via the ATIRE pathway is becoming increasingly evident in various cancers, including stomach cancer, esophageal squamous cell carcinoma, breast cancer, hepatocellular carcinoma, and CRC.

ADAR1, ADAR2, and ADAR3 are members of the ADAR family; while ADAR1 and ADAR2 are widely expressed, ADAR3 is primarily expressed in the brain and lacks catalytic activity. ADAR1 contains RNA-binding domains (RBDs) and Zα domains, whereas ADAR2 contains only RBDs. Zα domains enable ADAR1 to bind to newly synthesized RNA and inhibit the activation of pathogenic interferons (IFNs). ADAR1 has two isoforms: an IFN-inducible form (p150) and a constitutively expressed form (p110). It has been found that ADAR1-p110 reduces the chemotactic potential of melanoma cells and promotes immune exclusion . Loss of ADAR1 function results in unregulated RNA accumulation, which can be mistakenly recognized as foreign by RIG-I (Retinoic acid-inducible gene I), thereby triggering its activation and subsequent IFN response. Additionally, DNA released from damaged cells can activate the cGAS (GMP-AMP synthase)-STING (stimulator of interferon genes) pathway, leading to the production of type I IFNs through both pathways. The interaction between ADAR1 and the cGAS-STING and RIG-I pathways highlights a crucial balance in immune regulation. ADAR1's ability to interact with IFNs, regulate IFN production, and its complex roles in cancer therapy, along with its higher expression in MSI-H (microsatellite instability-high) patients, high TMB (tumor mutation burden), PD-1/PDL-1 levels, naive B cells, active memory CD4 T lymphocytes, and M1 macrophage cells, suggests its potential for modulating responses to cancer therapies. A potential mechanism has been proposed whereby increased ADAR1 expression in gastric cancer leads to proliferation and migration of various diseases through the mTOR/p70S6 kinase/S6 ribosomal protein pathway. To investigate the functional relationship between ADAR1 and mTOR signaling, the mTOR kinase inhibitor rapamycin was used to treat gastric cancer cells and observe its effects on ADAR1-overexpressed cell proliferation and migration. The results showed that ADAR1 overexpression significantly promoted cell proliferation and migration as expected, but these effects were significantly attenuated in cells treated with rapamycin. This suggests that rapamycin may block the effects of ADAR1 overexpression on gastric cancer cell growth and migration. These results indicate that the mTOR signaling pathway is important for ADAR1-mediated gastric cancer progression.

Recently, the effect of increased ADAR1 expression on survival in metastatic colon cancer was investigated. Both overall survival (OS) and relapse-free survival (RFS) were found to be significantly reduced in the group with increased ADAR1 expression; however, the study did not include patients with early-stage rectal cancer[20]. For all these reasons, the prognostic value of ADAR1 expression levels and/or changes in locally advanced rectal cancer patients for TNT response will be investigated.

Inclusion Criteria:

• Histological and staging diagnosis of local/locally advanced rectal cancer
• ECOG performance score between 0 and 2
• No contraindications for chemotherapy (CT) and/or radiotherapy (RT)

Exclusion Criteria:

• Those diagnosed with metastatic rectal cancer
• Those suspected of having rectal cancer or patients with a diagnosis of a second primary cancer
• Those who have not signed the informed consent form
• Those with contraindications for chemotherapy (CT) and/or radiation therapy (RT)

Patients diagnosed with locally advanced rectal cancer who presented to the medical oncology, radiation oncology, and general surgery clinics of Necmettin Erbakan University Faculty of Medicine Hospital.

All IPD that underlie results in a publication

It will be ready in September 2026 and can be shared within the following year.

The statistical methods used for objective response rates, survival data, and quality of life outcomes can be reviewed by an independent review.