June 04, 2026
Resection of locally recurrent rectal cancer remains a complex and challenging procedure, with negative margin (R0) resection being a critical indicator of long-term local control and overall survival (OS). Mayo Clinic surgeons rely on an evolving approach that often includes intraoperative radiation therapy (IORT) as an adjunct to achieve R0 resection.
"Advancements in imaging and technology, minimally invasive operative techniques, and increased integration of multidisciplinary specialists have made recurrent rectal cancer resection possible," says Amit Merchea, M.D., a colon and rectal surgeon at Mayo Clinic in Jacksonville, Florida. "Those factors also enable us to perform resections in a way that offers a reasonable quality of life and better long-term outcomes."
According to research published in Clinics in Colon and Rectal Surgery, the five-year OS for patients with locally recurrent rectal cancer is 50% when R0 resection is achieved. Five-year survival declines to 34% with R1 resection. Mayo Clinic surgeons understand the significance of complete resection and are prepared to use IORT as needed to achieve R0 status.
There is limited data available comparing OS with and without IORT during resection. But according to Dr. Merchea, the viability of IORT as an adjunct to resection depends on:
- Preoperative planning.
- Intraoperative margin assessment.
- Postoperative surveillance.
Integrating IORT into surgical preparation
Preparation for the potential inclusion of IORT begins long before the operation. Preoperative planning to predict whether IORT is appropriate and prepare for its use involves:
- Advanced imaging. High-resolution imaging helps predict margin positivity and evaluate tumor resectability.
- Multidisciplinary discussion. The tumor board meets to provide an understanding of the current disease and potential impact of aggressive oncological resection on functional outcomes and quality of life.
- Reirradiation. External beam radiation is often administered 2 to 3 weeks before surgery to anyone at risk of a positive margin. The radiation boost retreats the area at risk to optimize margins and primes tissues for IORT.
According to an article published by Mayo Clinic radiation oncologist Michael S. Rutenberg, M.D., Ph.D., and colleagues in Practical Radiation Oncology, preoperative reirradiation has been shown to improve R0 resection rates. It also is associated with enhanced long-term disease control.
Using frozen section pathology to determine the need for IORT
Final decisions about the indication and potential benefit of IORT are made intraoperatively using frozen section pathology — a technique pioneered at Mayo Clinic. Following initial tumor resection, a tissue sample is sent to an on-site frozen section pathology lab, where a subspecialized pathologist assesses margin status:
- Negative margins negate the need for IORT.
- Close or positive margins require collaboration between the surgeon and radiation oncologist to determine whether to proceed with further resection or administer IORT.
"IORT allows us to deliver targeted radiation directly to an area where the tumor margin is close or microscopically positive," says Dr. Rutenberg. "It provides an additional method of treatment to ensure local disease control. Because the dose is localized and most normal tissue is displaced at the time of irradiation, the morbidity of the additional radiation is limited."
While Mayo Clinic surgeons and oncologists plan for IORT in approximately 80% of patients, they deliver it only 60% of the time.
Following strict surveillance protocol after resection
Recurrence following resection is concerning. Distant recurrence can affect up to 25% of patients after treatment for recurrent cancer. Local recurrence — in the area where IORT was delivered or anywhere within the pelvis — ranges between 5% and 15%, depending on:
- Margin status after resection.
- Nature of the initial recurrence.
- Type of cancer.
"Greater than 90% of recurrences occur within the first two years following resection," says Dr. Merchea. "Surveillance during those years is critical."
Postoperative surveillance protocol at Mayo Clinic comprises:
- Blood tests administered every 3 to 6 months to check for tumor markers, such as carcinoembryonic antigen and circulating tumor DNA.
- Imaging, including a pelvic MRI and CT of the chest, abdomen and pelvis performed every three months for the first two years.
- Colonoscopy performed at one year, with the need for subsequent colonoscopies dependent upon findings.
The goal of surveillance is to detect cancer recurrence early when intervention is more likely to be effective. According to Dr. Merchea, a substantial proportion of patients with recurrent rectal cancer are candidates for resection. However, timely referral to a high-volume center is critical for optimizing survival outcomes and recovery.
"When rectal cancer recurs, it's important that patients are seen by a colorectal surgeon," says Dr. Merchea. "With multidisciplinary input, the specialist can most accurately determine resectability and help guide the optimal treatment plan."
For more information
Amarnath SR. The role of intraoperative radiotherapy treatment of locally advanced rectal cancer. Clinics in Colon and Rectal Surgery. 2023;37:239.
Rutenberg MS, et al. Reirradiation in the management of locally recurrent rectal adenocarcinoma. Practical Radiation Oncology. 2025;15:e166.
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